GB2519950A

GB2519950A - An Inhaler

Info

Publication number: GB2519950A
Application number: GB1319152.3A
Authority: GB
Inventors: Julia Greenwood; Simon James Smith; Clement Carl; Georgina Koffler
Original assignee: British American Tobacco Investments Ltd; British American Tobacco Co Ltd
Current assignee: British American Tobacco Investments Ltd
Priority date: 2013-10-30
Filing date: 2013-10-30
Publication date: 2015-05-13
Also published as: GB201319152D0

Abstract

An inhaler 1 comprising a first 10A and second 10B plenum chamber containing a pressurised propellant fluid and an equalising member 12 located in fluid communication between them, a formulation chamber 9 for containing a fluid to be inhaled and having a chamber outlet 8A with a valve 19 therein for the release of formulation fluid for inhalation by a user when the valve is open, wherein the equalisation member is configured to equalise the pressure between the second plenum chamber and the formulation chamber by allowing fluid to flow from the first plenum chamber to the second plenum chamber, in order to restore the pressure in the formulation chamber to above a predetermined pressure set-point in response to a pressure drop in the formulation chamber below the pressure set-point due to a release of formulation fluid from the formulation chamber. The equalising member can be a pressure controlling device, such as a membrane or diaphragm such that the flow of fluid from the first plenum chamber to the second plenum chamber is restricted so that it takes a predetermined period of time for the pressure in the formulation chamber to be restored to a pressure set-point.

Description

An Inhaler

Field of the Invention

The present invention relates to an inhaler for administering a substance or formulittion by inhalation and to a method of controlling the delivery of a substance or formtflation from an inha'er. The substance or formifiation may contain nicotine and the inhaler may take the form of a nicotine delivery system. The invention also relates to a cartridge for containing a substance or formulation.

Background

Inhalers are known that comprise a mouthpiece, an actuator and a compartment containing a formulation for inhalation. Upon actuation of the actuator by a user, formulation is released from the compartment and is expelled through the mouthpiece for inhalation by the user. Is

Summary

According to the invention, there is provided an inha'er comprising a first plenum chamber for containing a pressurised fluid, a formulation chamber for containing a formiflation fluid for inhalation and having a chamber ouflet with a va've therein for the release of formulation fluid therefrom for inhalation by a user when the valve is open, an intermediate chamber, an equalisation member that seats the intermediate chamber from one of the fonrnflation chamber and the first p'enum chamber and is configured to equaBse the pressure in the intermediate chamber and the one of the formiflation chamber and the first plenum chamber, and a passage to provide fluid communication between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber so that fluid will flow between the intermediate chamber and the other one of the formulation chamber and the first p'enum chamber to restore the pressure in the formiflation chamber to a pressure above a pressure set-point in response to a pressure drop in the formulation chamber to below the pressure set-point due to a release of formulation fluid from the formu'ation chamber.

In one embodiment, the flow resistance of the passage is selected such that the rate of flow of fluid between the intermediate chamber and the other one of the formulation s chamber and the first p'enum chamber is restricted so that, following a pressure drop in the formidation chamber, the pressure in the formtflation chamber is graduafly restored to a pressure above the pressure set-point. The flow resistance of the passage may be selected such that the rate at which the pressure in the formulation chamber is gradually restored is s'ower than the rate at which the pressure in the formulation chamber drops when formulation fluid is released from the formu'ation chamber, so that it takes a predetermined period of time for the pressure in the formulation chamber to be restored to a pressure above the pressure set-point.

In one embodiment, the combined volume of the intermediate chamber and the one of the formulation chamber and first plenum chamber is constant, and the equalisation io member forms a boundary therebetween that adjusts to after the relative volumes of the intermediate chamber and the one of the formuthtion chamber and first plenum chamber to equalise the pressures therein.

In one embodiment, the intermediate chamber comprises a second plenum chamber that is is suitable for containing a pressurised fUnd and the equalisation member seats the formulation chamber from the second plenum chamber and is configured to equalise the pressure in the formulation and second plenum chambers, and wherein the passage provides fluid communication between the second plenum chamber and the first plenum chamber so that pressurised fluid in the first plenum chamber flows into the second plenum chamber to restore the pressure in the second plenum chamber and in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber and in the second plenum chamber to below said pressure set-point due to a release of formulation fluid from the formulation chamber.

In one embodiment, the equalisation member comprises a flexible diaphragm of impermeable material that separates the formulation chamber from the second plenum chamber and deforms to equalise the pressure in the formulation and second plenum chambers. The flexiNe diaphragm may comprise a bag, the formulation chamber being o defined by the interior of the bag and the second plenum chamber being defined by the exterior of the bag such that pressurised fluid in the second plenum chamber exerts a force on the formulation fluid in the formulation chamber through the bag.

Alternativ&y, the formubtion chamber may be defined by the exterior of the bag and the second plenum chamber being defined by the interior of the bag such that pressurised fluid in the second plenum chamber exerts a force on the formulation fluid in the formulation chamber through the bag. In one such embodiment, the first plenum chamber is also defined by the interior of the bag and the bag further comprises a constriction that is disposed between the second plenum chamber and the first plenum chamber and comprises the passage that provides fluidly communication between the first and second p'enum chambers.

In an alternate embodiment, the equalisation member comprises a piston that separates the formulation chamber and the second plenum chamber, said piston being slideable to adjust the relative volumes of the formulation and second plenum chambers to equalise the pressures therein. I0

In another embodiment, the intermediate chamber is suitable for containing a formulation fluid for inhalation and the equalisation member seals the intermediate chamber from the first plenum chamber and is configured to equalise the pressure in the intermediate and first plenum chambers, and wherein the passage provides fluid communication between the formulation chamber and the intermediate chamber so that formulation fluid in the intermediate chamber flows into the formuthtion chamber to restore the pressure in the formuhition chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber to below said pressure set-point due to a release of formulation fluid from the formulation chamber.

In one embodiment, the equalisation member comprises a flexible diaphragm of impermeable material that separates the intermediate chamber from the first plenum chamber and deforms to equalise the pressure in the intermediate and first plenum chambers. The flexible diaphragm may comprise a bag, the formulation chamber and the intermediate chamber being defined by the interior of the bag and the first plenum chamber being defined by a portion of the exterior of the bag such that pressurised fluid in the first plenum chamber exerts a force on the formulation fluid in the intermediate chamber through said portion of the bag. In one such embodiment, the bag further comprises a constriction that is disposed between the formulation chamber and the intermediate chamber and comprises the passage that provides fluiffly communication between the formuhition and intermediate chambers. The first plenum chamber may be sealed from the portion of the bag that forms the form&ation chamber.

In one embodiment, the inhaler comprises an actuating mechanism including an actuator and an actuation valve, the actuation valve being moveable from a closed position to an open position in response to actuation of the actuator by the user to unblock the chamber outlet. The inhaler may comprise a biasing means that is configured to bias the actuation valve into the closed position.

In one embodiment, the actuator comprises a diaphragm that deforms to move the actuation valve into the open position in response to inhalation by the user. In one such embodiment, the diaphragm partitions the inside of the housing into first and second compartments and one of the first and second compartments comprises a suction channel so that the diaphragm deforms in response to the application of suction to the suction channel. I0

In an alternate embodiment, the actuator comprises a button that is depressible by the user to move the actuation valve into said open position. In one such embodiment, the inhaler comprises a lever and the actuation valve comprises a valve head and a valve seat and is configured so that when the actuation valve is in the closed position the valve stem receives the valve head to block the chamber outlet, and wherein the lever engages with the va've head and the actuator is depressible inwardly towards the longitudinal axis of the outer housing to cooperate with the lever to urge the valve head away from the valve stem to move the actuation valve to the open position to unblock the chamber outlet.

In one embodiment, the valve comprises the actuating valve. In an alternate embodiment, the valve comprises a pressure relief valve that is configured to open when the pressure in the formulation chamber is above said pressure set-point.

In one embodiment, the pressure relief valve comprises a valve housing and a valve head that is slidable within the valve housing between first, second and third positions, wherein in the first and second positions the valve head is configured to block the chamber outlet and in the third position the valve head is configured to unblock the chamber oirdct, the valve head being moveable from the first position to the second position upon inhahition by the user and moveabe from the second position to the third position under the influence of the pressure of the formulation fluid in the formulation chamber, when said pressure is above said pressure set-point. In one such embodiment, the pressure rehef valve comprises a suction channel disposed on an opposite side of the valve head to the chamber outlet and configured so that when a user inhales through the suction channel a force is exerted on the valve head that urges the valve head away from its first position.

In one embodiment, when the valve head is in the first position a reduced surface area of the valve head is fluidly communicated with the chamber outlet, and wherein when the valve head is in the second and third positions an increased surface area of the valve head is fluiffly communicated with the chamber outlet. In one such embodiment, the pressure relief valve comprises a valve seat that surrounds the periphery of the chamber outlet and the valve head is urged against the valve seat in said first position so that a reduced surface area of the valve head is fluidly communicated with the chamber outlet, an increased surface area of the valve head being fluidly communicated with the chamber outlet when the valve head is in the second and third positions. I0

In one embodiment, the valve head comprises a first section of reduced cross-section that comprises a first face and a second section of increased cross-section that comprises a second face, and wherein when the valve head is in the first position the first face is fluidly communicated with the chamber outlet and the second face is sealed therefrom and when the valve head is in the second and third positions the first and second faces are both fluiWy communicated wIth the chamber ouflet. In one such embodiment, the valve housing comprises a first section of reduced cross-section that is proximate to the chamber outlet and a second section of increased cross-section that is remote to the chamber outlet, and wherein when the valve head is in the first position the first section of the valve head is received in the first section of the valve housing to seal against the inside surface thereof to seal the second face from the chamber outlet, and wherein when the valve head in the second and third positions the first section of the valve head is received in the second section of the valve housing to provide fluid communication between the second surface and the chamber outlet.

In one embodiment, the valve housing comprises a peripheral wall and an outlet channel to vent the formulation fluid from the inhaler for inhalation by the user, wherein when the valve head is in the first and second positions the valve head seals against the peripheral wall of the valve housing to seal the chamber outlet from the o otiflet channd, and wherein when the valve head is in the third position the ouflet channel is fluidly communicated wIth the chamber outlet. The pressure reHef valve may comprise a biasing means to bias the pressure relief valve into the first position.

In one embodiment, the inhaler comprises a cartridge having a partitioning wall, wherein the formulation chamber, intermediate chamber and first plenum chamber are formed in the cartridge and the partitioning wall separates the intermediate chamber from the other one of the formulation chamber and the first plenum chamber, wherein the passage that fluidly communicates the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is formed in said partitioning wall. The cartridge may be removably received in the housing.

The invention also provides a cartridge for an inhaler comprising a first plenum chamber for containing a pressurised fluid, a formulation chamber for containing a formulation fluid for inhalation and having a chamber outlet for the release of formulation fluid therefrom for inhalation by a user when a valve is open, an io intermediate chamber, an equaBsation member that seals the intermediate chamber from one of the formulation chamber and the first plenum chamber and is configured to equalise the pressure in the intermediate chamber and the one of the formulation chamber and the first plenum chamber, and a passage to provide fluid communication between the intermediate chamber and the other one of the formulation chamber and the first pknum chamber so that thud will flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber to restore the pressure in the formulation chamber to a pressure above a pressure set-point in response to a pressure drop in the formulation chamber to below said pressure set-point due to a release of formulation fluid from the formulation chamber.

In one embodiment, the flow resistance of the passage is selected such that the rate of flow of fluid between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is restricted so that, following a pressure drop in the formulation chamber, the pressure in the formulation chamber is gradually restored to a pressure above said pressure set-point. The flow resistance of the passage may be selected such that the rate at which the pressure in the formulation chamber is gradually restored is slower than the rate at which the pressure in the formulation chamber drops when formulation fluid is released from the formulation chamber, so that it takes a predetermined period of time for the pressure in the formulation chamber to be restored to a pressure above said pressure set-point.

In one embodiment, the combined volume of the intermediate chamber and the one of the formulation chamber and first plenum chamber is constant, and the equalisation member forms a boundary therebetween that adjusts to alter the relative volumes of the intermediate chamber and the one of the formulation chamber and first plenum chamber to equalise the pressures therein.

In one embodiment, the intermediate chamber is suitable for containing a pressurised fluid and the equalisation member seals the formulation chamber from the intermediate chamber and is configured to equabse the pressure in the formulation and intermediate chambers, and wherein the passage provides fluid communication between the intermediate chamber and the first plenum chamber so that pressurised fluid in the first plenum chamber flows into the intermediate chamber to restore the pressure in the intermediate chamber and in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation io chamber and in the intermediate chamber to bdow said pressure set-point due to a release of formiflation fluid from the formdation chamber.

In one such embodiment, the equalisation member comprises a flexible diaphragm of impermeable material that separates the formulation chamber from the intermediate chamber and deforms to equalise the pressure in the formu ation and intermediate chambers. The flexible diaphragm may comprises a bag, the formulation chamber being defined by the interior of the bag and the intermediate chamber being defined by the exterior of the bag such that pressurised fluid in the intermediate chamber exerts a force on the formulation fluid in the formulation chamber through the bag.

Alternatively, the formulation chamber may be defined by the exterior of the bag and the intermediate chamber being defined by the interior of the bag such that pressurised fluid in the intermediate chamber exerts a force on the formulation fluid in the formulation chamber through the bag. In such an embodiment, the first plenum chamber may also be defined by the interior of the bag and the bag further comprises a constriction that is disposed between the intermediate chamber and the first plenum chamber and comprises the passage that provides fluidly communication between the intermediate and first plenum chambers.

In an alternate embodiment, the equalisation member comprises a piston that separates the formifiation chamber and the intermediate chamber, said piston being shdeable to adjust the r&ative volumes of the formulation and intermediate chambers to equahse the pressures therein.

In one embodiment, the intermediate chamber is suitable for containing a formulation fluid for inhalation and the equalisation member seals the intermediate chamber from the first plenum chamber and is configured to equalise the pressure in the intermediate and first plenum chambers, and wherein the passage provides fluid communication between the formulation chamber and the intermediate chamber so that formulation fluid in the intermediate chamber flows into the formulation chamber to restore the pressure in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber to below said pressure set-point due to a release of formulation fluid from the formulation chamber.

In one such embodiment, the equalisation member comprises a flexible diaphragm of impermeable material that separates the intermediate chamber from the first plenum io chamber and deforms to equalise the pressure in the intermediate and first plenum chambers. The flexible diaphragm may comprise a bag, the formifiation chamber and the intermediate chamber being defined by the interior of the bag and the first plenum chamber being defined by a portion of the exterior of the bag such that pressurised fluid in the first plenum chamber exerts a force on the formulation fluid in the intermediate chamber through said portion of the bag. The bag may further comprise a constriction that is disposed between the formulation chamber and the intermediate chamber and comprises the passage that provides fluidly communication between the formulation and intermediate chambers.

The first plenum chamber may be sealed from the section of the bag that forms the formulation chamber.

In one embodiment, the cartridge comprises a partitioning wall that separates the intermediate chamber from the other one of the formulation chamber and the first plenum chamber, wherein the passage that fluidly communicates the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is formed in said partitioning wall.

The invention &so provides a nicotine delivery system comprising the inhaler according o to the invention.

The invention also provides a method of controlling the delivery of formiflation fluid from an inhaler comprising the steps of: providing formulation fluid for inhalation in a formulation chamber at a pressure above a pressure set-point required to release formulation fluid therefrom for inhalation by a user; providing pressurised fluid in a first plenum chamber at a pressure above the pressure set-point, the pressure in one of the first plenum chamber and the formulation chamber being equalised with the pressure in an intermediate chamber by an equalisation member; releasing formulation fluid from the formiflation chamber in response to inhalation by a user so that the pressure therein drops to below the pressure set-point; and, aflowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber to restore the pressure in the formulation chamber to a pressure above the pressure set-point.

In one embodiment, the step of allowing fluid to flow between the intermediate io chamber and the other one of the formifiation chamber and the first plenum chamber to restore the pressure in the formuthtion chamber comprises allowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber at a restricted rate of flow so that the pressure in the formulation chamber is gradually restored to a pressure above the pressure set-point.

In one embodiment, the step of allowing fluid to flow between the intermediate chamber and the other one of the formubtion chamber and the first plenum chamber at a restricted rate of flow comprises allowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber at a flow rate at which the rate at which the pressure in the formulation chamber is gradually restored is slower than the rate at which the pressure in the formulation chamber drops when formulation fluid is released from the formulation chamber, so that it takes a predetermined period of time for the pressure in the formulation chamber to be restored to a pressure above the pressure set-point.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of an inhaler according to a first embodimcnt of the invention; Figure 2 is a front view of the inhaler of Figure 1; Figure 3 is a perspective view of the inhaler of Figure 1, with a portion of an outer housing removed; Figure 4 is a cross-sectional perspective view of the inhaler of Figure 1; Figure 5 is a cross-sectional side view of the inhaler of Figure 1; -10-Figure 6 is a close-up cross-sectional side view of an actuation valve of the inhaler of Figure 1, in a closed position; Figure 7 is a close-up cross-sectiona' side view of the actuation va've of Figure 6, in an open position; Figure 8 is a perspective view of an inhaler according to a second embodiment of the invention, with a portion of an outer housing removed; Figure 9 is a close-up cross-sectional side view of an actuation valve of the inhaler of Figure 8, in a closed position; Figure 10 is a close-up cross-sectional side view of the actuation valve of Figure 9, in an io open position; Figure 11 is a cross-sectional side view of an inha'er according to a third embodiment of the invention; Figure 12 is a close-tip cross-sectional side view of a pressure relief valve of the inhaler of Figure 11, in a first position; Figure 13 is a close-up cross-sectional side view of the pressure rehef valve of Figure 12, in a second position; Figure 14 is a close-up cross-sectional side view of the pressure relief valve of Figure 12, in a third position; Figure 15 is a close-up cross-sectional side view of a pressure relief valve of an inhaler according to a fourth embodiment of the invention, in a first position; Figure 16 is a close-up cross-sectional side view of the pressure relief valve of Figure 15, in a second position; Figure 17 is a close-up cross-sectional side view of the pressure relief valve of Figure 15, in a third position; Figure iS is a close-up cross-sectional side view of a pressure relief valve of an inhaler according to a fifth embodiment of the invention, in a first position; Figure 19 is a close-tip cross-sectional side view of the pressure relief valve of Figure i8, in a second position; Figure 20 is a close-up cross-sectional sidc view of the pressure relief valve of Figure i8, in a third position; Figure 21 is a close-up cross-sectional side view of an inhaler according to a sixth embodiment of the invention, with an actuation valve in a first position; and, Figure 22 is a close-up cross-sectional side view of the inhaler of Figure 21, with the actuation valve in a second position.

Detailed Description

-11 -Referring to Figures 1-7, an inhaler 1 according to a first embodiment of the invention is shown. The inhaler 1 maybe a nicotine delivery system that may be used as a substitute for cigarette, cigar or Bke smoking article. The inhaler 1 comprises an outer housing 2 and an actuating mechanism 3. The outer housing 2 comprises an effiptical cylinder shaped body 4 with a mouthpiece 5 at one end thereof having a formulation outlet 6A and a suction outlet 6B therein.

The actuating mechanism 3 comprises an actuator is and an actuation valve 17. The actuator 15 comprises a diaphragm 16 that is pivotally mounted to an end of the outer io housing 2 that is distal to the mouthpieces. The diaphragm i6 is disposed in an inner space 7 in the body 4 and partitions said space 7 into first and second compartments 7A, 7B. The diaphragm i6 seals the first compartment 7A from the second compartment 7B and a cartridge 8 is disposed in the first compartment 7A.

The cartridge 8 comprises a formifiation chamber 9, a first plenum chamber bA, and an intermediate chamber comprising a second p'enum chamber ioB. The formulation chamber 9 contains a form&ation for inhalation that is pressurised so that it is above atmospheric pressure. The formulation chamber 9 is sealed at one end by an equalisation member comprising a piston ii that is slidably received in the cartridge 8 and the opposing end of the formulation chamber 9 comprises a cartridge outlet 8A.

The first plenum chamber ioA is disposed towards an end of the cartridge 8 that is remote of the cartridge outlet 8A and the second plenum chamber ioB is disposed between the formulation chamber 9 and the first plenum chamber bA, on the opposite side of the piston ii to the formulation chamber 9. The first and second plenum chambers bA, loB are separated by a partitioning wall 12 and a passage 13 is formed therein to fluidly communicate the first plenum chamber ioA with the second plenum chamber loB.

An ouflet channd 14 fluidly communicates the cartridge ouflet 8A with the mouthpiece formulation outlet 6A. The actuation valve 17 is configured to sàlectiv&y block/unblock the ouflet channel 14 so that formulation may be salectively supplied to the mouthpiece formulation outlet 6A from the formuflation chamber 9 for inhalation by the user. The actuation valve 17 comprises a valve seat 18 and a valve head 19. The valve seat 18 is disposed in the outlet channel 14 and is configured to receive the valve head 19 to form a seal therebetween. The valve head 19 is mounted to the diaphragm 16 and rests -12 -against the valve seat 18 to block the outlet channel 14 when the actuation valve 17 is in a closed position (as shown in Figure 6). The actuation valve 17 is moveable to an open position wherein the valve head 19 is urged away from the valve seat 18 so that the ouflet chann& 14 is unblocked (as shown in Figure 7).A first biasing means 20, for example, a spring or portion of resilient material, is provided between the diaphragm 16 and the outer housing 2 to urge the diaphragm 16 towards the longitudinal axis of the outer housing 2 so that the valve head 19 is urged towards the valve seat i8 to bias the actuation valve 17 into the closed position.

io The inside of the first compartment 7A is sealed from the inside of the cartridge 8 and the ouflet channel 14 and the inside of the second compartment 7B is fluidly communicated with the end of the mouthpiece 5 by the suction outlet 6B. Therefore, when the user sucks on the mouthpiece 5 to inhale formulation through the formulation outlet 6A, air in the second compartment 7B is sucked through the suction otiflet 6B so that the pressure in the second compartment 7B reduces to less than the pressure in the first compartment 5A. The pressure difference between the first and second compartments 7A, 7B causes a force to be exerted on the diaphragm i6 in a direction transverse the longitudinal axis of the outer housing 2 that is sufficient to overcome the force of the first biasing means 20 so that the diaphragm i6 pivots in a direction away from the longitudinal axis and the valve head 19 is urged away from the valve seat 18 to open the actuation valve 17.

A pressure relief valve 21 is disposed in the outlet channel 14, between the actuation valve 17 and the formulation outlet 6A, and is configured to permit the flow of formulation from the formulation chamber 9 to the formulation outlet 6A when the pressure of the formulation in the outlet channel 14 on the formulation chamber 9 side of the pressure relief valve 21 reaches a pressure set-point, providing the actuation valve 17 is in its open position. The pressure release valve 21 comprises a valve ball 22, a second valve scat 23 and a second biasing means 24. The second valve seat 23 comprises a portion of the outlet channd 14 that is of a reduced cross-sectional area so that it has a diameter smaer than the diameter of the valve ball 22. The valve ball 22 is disposed between the form&ation ouflet 6A and the second valve seat 23 and is biased theretowards by the second biasing means 24. Therefore, when the pressure in the outlet channel 14 on the chamber outlet 8A side of the pressure relief valve 21 is less that the pressure set-point, the second biasing means 24 urges the valve ball 22 against the second valve seat 23 to prevent fluid from flowing through the outlet channel 14.

-13 -When the pressure in the outlet channel 14 on the chamber outlet 8A side of the pressure relief valve 21 is above the pressure set-point, the pressure of the formulation is sufficient to exert a force on the valve ball 22 that overcomes the force of the second biasing means 24 so that the pressure r&ief valve 21 is urged into an open position wherein the valve ball 22 is urged away from the second valve seat 23 so that a gap is formed therebetween that allows for formulation to flow through the outlet channel 14.

The first and second plenum chambers bA, loB contain a pressurised liquid or gas.

The pressurised gas in the second plenum chamber loB exerts a force on the piston 11 io that urges the piston 11 towards the cartridge outlet 8A in the ongitudinal direction of the outer housing. When the piston 11 moves towards the cartridge outkt 8A, the volume of the formulation chamber 9 decreases and therefore the pressure of the formulation contained therein increases. Similarly, when the piston 11 moves towards the cartridge outlet 8A the volume of the second plenum chamber ioB increases and therefore the pressure of the gas contained therein decreases. The piston ii will move within the cartridge 8 until the pressures in the formuthtion chamber 9 and second p'enum chamber loB are equal. Thus, the combined volume of the formulation and second plenum chambers 9, loB is fixed and the piston 11 is configured to form a boundary therebetween that is moveable to adjust the relative volumes of formulation and second plenum chambers 9, loB to equalise the pressures therein. The second plenum chamber ioB is fluidly communicated with the first plenum chamber ioA so that when the piston 11 is moved towards the cartridge outlet 8A and the pressure in the second plenum chamber ioB decreases, gas will flow from the first plenum chamber bA to the second plenum chamber ioB until the pressures therein are equal.

Therefore, the piston ii will slide to a position wherein the pressure in the formulation chamber 9 and first and second plenum chambers ioA, ioB are equal. The gas in the first and second plenum chambers bA, loB is pressurised to be above the pressure set-point required to open the pressure relief valve 21, and therefore the pressure of the formu'ation in the formulation chamber 9 will also be h&d at a pressure above the pressure set-point by the force of the piston ii being urged towards the cartridge outlet 8A.

In use, the user inhales to urge the diaphragm 16 away from the longitudinal axis of the outer housing 2 to open the actuation valve 17 and unblock the outlet channel 14 in the manner previously described, resulting in the inside of the formulation chamber 9 being fluidly communicated with the pressure relief valve 21. As the pressure of the formulation in the formulation chamber 9 is initially above the pressure set-point, the pressure relief valve 21 will open and formulation will flow through the outlet channel 14 to be expelled out of the formulation outlet 6A of the mouthpiece 5 for inhalation by the user. When formulation is expelled from the formulation chamber 9, the pressure therein will decrease and the piston 11 will slide towards the cartridge outlet 8A under the force of the pressure in the second plenum chamber ioB until the pressures in the formulation chamber 9 and second plenum chamber loB equalise. The piston ii will continue to slide towards the cartridge outlet 8A and formulation will continue to be expelled out of the formulation outlet 6A from the formulation chamber 9 until the io equalised pressure in the formulation chamber 9 and second plenum chamber loB is less than the pressure set-point required to open the pressure reBef valve 21, at which point the pressure relief valve 21 will close.

When the piston 11 is slid towards the cartridge outlet 8A in response to the release of formulation from the formu ation chamber 9, the pressurised gas in the first plenum chamber bA flows through the passage 13 and into the second p'enum chamber ioB to increase the pressure therein until the pressures in the first and second plenum chambers bA, loB are equalised. This will cause the pressure in the second plenum chamber ioB to urge the piston 11 towards the cartridge outlet 8A until the pressures in the formulation chamber 9 and the first and second plenum chambers ioA, ioB are all equalised and are at a pressure above the pressure set-point. The user may then again inhale to reopen the actuation valve 17, resulting in the pressure of the formulation in the formulation chamber 9 opening the pressure relief valve 21 and formulation being expelled out of the formulation outlet 6A of the mouthpiece 5 for inhalation by the user.

Formulation will continue to be expelled from the formulation chamber 109 until the pressure therein is less than the pressure set-point required to open the pressure relief valve 21, at which point the pressure relief valve 21 will close. As formulation is only released from the formulation chamber 9 whilst the pressure therein is above the pressure set-point, each inhalation by the user will result in an incremental movement of the piston 11 towards the cartridge outlet 8A and therefore a metered dosage of formulation being expefled from the inhaler. The process of r&easing dosages of formulation may be repeated until the formulation is dep'eted, the piston 11 is slid within the cartridge 8 to a position wherein it abuts the cartridge ouflet 8A, or the equalised pressures in the formulation chamber 9 and the first and second plenum chambers bA, loB is less than the pressure set-point required to open the pressure relief valve 21.

-15 -The passage 13 has a small diameter so that is has a large flow resistance, resulting in a low flow rate of the pressurised gas flowing between the first and second plenum chambers bA, loB during equalisation thereof. Therefore, when the pressure in the second plenum chamber ioB is less than the pressure set-point of the pressure rehef valve 21 due to the release of formulation from the formulation chamber 9, the gas in the first plenum chamber ioA will flow into the second plenum chamber ioB gradually.

Thus, it will take a certain period of time for first and second plenum chambers bA, loB to equalise so that the formulation and second plenum chambers 9, loB are re-pressurised to above the pressure set-point required to open the pressure relief valve 21 io and so, after inhalation of the formulation, the user must wait said period of time before another dosage of formulation may be rdeased for inhalation. This means that the inhaler has the advantage of releasing metered dosage of formulation with a time delay between successive dosages to ensure that the user may not consume more than a pre-determined amount of formulation within a certain time period.

Although in the above described embodiment the first p'enum chamber ioA is provided in the cartridge and is separated from the second plenum chamber by a peripheral wall, in an alternate embodiment (not shown), the first plenum chamber is provided in a separate container. In such an embodiment, the first and second plenum chambers may be fluidly communicated by, for example, a passage provided in the housing or section of pipe that comprises the passage. In yet another embodiment (not shown), the first plenum chamber or the formulation and second plenum chambers are provided in the inner space, between the outer housing and the cartridge, and the passage is provided in a wall of the cartridge to fluidly communicate the first and second plenum chambers.

In such an embodiment, it would be necessary to seal the inner space between the cartridge and the housing from the atmosphere to prevent leakage of the pressurised gas/formulation.

Aithough in the above described embodiment the passage 13 has a arge flow resistance as a result of having a small diameter, in akernate embodiments (not shown) the passage may have a large flow resistance as a result of having a large ength or as a result of comprising protrusions inside the passage to induce a turbiflent flow regime.

In yet another embodiment, a portion of porous material, for examp'e, loam or cellulose fibre, maybe provided in the passage to increase the flow resistance thereof.

In one embodiment, the volume of the first plenum chamber mA is significantly larger than the volume of the second plenum chamber loB so that a large volume of pressurised gas can be stored in the first plenum chamber bA to re-pressurise the second plenum chamber loB upon rdease of formulation from the formulation chamber 9 for inhalation. Such an embodiment would increase the number of times the second plenum chamber toB may be re-pressurised to a pressure greater than the pressure set-point to increase the amount of times that the inhaler 1 may be actuated by the user to release formulation for inhalation in comparison to inhalers having a smaller first plenum chamber. I0

Although in the above described embodiment the actuation valve 17 comprises a valve head 19 that is attached to the diaphragm i6 and is configured to be received against a valve seat i8 to selectively block the outlet channel, it should be recognised that other actuation valve configurations are intended to fall within the scope of the invention. For example, the actuation valve may comprise a pinch valve, having a flexib'e condtut that fluidly communicates the cartridge ouflet with the pressure relief valve. In one such an embodiment, a member provided on the diaphragm pinches the flexible conduit dosed when the actuation valve is in the closed position so that no fluid may flow therethrough. When the user inhales so that the diaphragm is urged away from the longitudinal axis of the outer housing, the member moves away from the flexible conduit so that the flexible conduit is no longer pinched shut and so opens to fluidly communicate the cartridge outlet with the pressure relief valve.

Although in the above described embodiment the pressure relief valve 21 comprises a valve ball 22 that is urged towards second valve seat 23 by a second biasing means 24, in alternate embodiments (not shown) the pressure relief valve 21 may be of a different configuration. For example, the pressure relief valve may comprise a static insert and a sliding insert that are moved relative to each other to open and close the pressure relief valve. In onc such embodiment, the sliding insert is slidably received in the outlet channel towards the formulation ouflet end thereof. The sliding insert comprises an aperture therein that, in use, vents to the inside of the user's mouth. The static insert comprises an insert passage and a face that faces towards the formulation outlet. The static insert is disposed in the outlet channel between the cartridge ouflet and the sliding insert and the sliding insert is urged against the face of the static insert by a third biasing means so that the aperture is blocked by the face. When the actuation valve is opened by the user, the pressure of the formulation in the outlet channel -17-overcomes the force of the third biasing means so that the siding insert is urged away from the face of the static insert so that a gap is formed therebetween, allowing for formulation to flow from the cartridge, through the insert passage and out of the ouflet aperture, via the gap formed between the static and sBding inserts, whereupon in may be inhaled by the user.

Although in the above described embodiment the diaphragm i6 is urged towards the longitudinal axis of the outer housing 2 by a first biasing means 20 that provides a biasing force to urge the valve head 19 towards the valve seat 18 to bias the actuation io valve 17 into the dosed position, in an alternate embodiment (not shown) the first biasing means is omitted and instead the diaphragm is manufactured from a resilient material that provides the biasing force. It should be recognised that the biasing force may also be provided solely by a pressure differential between the first and second compartments 7A, 7B. For example, if the first compartment 7A is sealed from the atmosphere the pressures in the first and second compartments 7A, 7B will be equal until the user inhales to draw air out of the second compartment 7B, via the suction ouflet 6B, whereupon the diaphragm 16 will be urged away from the longitudinal axis of the outer housing 2so that the volume of the second compartment 7A decreases. This will result in the volume of the first compartment 7A increasing and the pressure therein decreasing. Therefore, when the user removes the mouthpiece 5 from their mouth so that air may pass into the second compartment 7B, the diaphragm 16 will be urged back towards the longitudinal axis so that the volume of the first compartment 7A reduces until the pressures in the first and second compartments 7A, 7B equalise. In alternative embodiments, the biasing force may be provided solely by the resilience of the diaphragm or a biasing member, in which case a ventilation aperture (not shown) may be provided in the outer housing 2 to fluidly communicate the inside of the first compartment 7A with the atmosphere to facilitate movement of the diaphragm i6.

Aithough in the above described embodiment the first biasing means 20 is positioned o between the diaphragm 16 and the housing 2 to urge the diaphragm to pivot towards the longitudinal axis of the outer housing 2, in an alternate embodiment (not shown) the first biasing means comprises a torsion spring that pivotally mounts the diaphragm to the outer housing and is configured to bias the diaphragm towards the longitudinal aids. -18-

Although in the above described embodiment the diaphragm 16 is pivotally mounted to the inside of the outer housing 2 to provide movement therebetween upon inhalation by the user to actuate the actuation valve 17, in an alternate embodiment (not shown) the diaphragm is manufactured from a flexible material, for examp'e, nibber or plastic, and inhalation by the user causes the diaphragm to deform so that a portion thereof moves away from the longitudinal axis of the outer housing to actuate the valve.

Although in the above described embodiment the actuator 15 comprises a diaphragm i6 that is actuated upon inhalation by the user, in alternate embodiments (not shown) the io diaphragm is omitted and repthced by an actuator comprising a button that is actuated by the user to open the actuation valve. In one such embodiment, the actuator comprises a push button that is attached to one end of a lever and the other end of the lever is attached to the valve head so that upon depression of the button by the user the valve head is urged away from the valve seat to open the actuation valve.

Although in the above described embodiment the actuator 15 is configured so that the diaphragm 16 is urged away from the longitudinal axis of the outer housing 2 upon inhalation by the user, in an alternate embodiment (not shown) the diaphragm 16 is configured to be urged towards the longitudinal axis upon inhalation. For example, the second compartment 7B may be sealed and instead the inside of the first compartment 5A is fluidly communicated with the suction outlet 6B so that when the user inhales the pressure in the first compartment 7A becomes less than the pressure in the second compartment 7B to deform the diaphragm 16 so that it is urged against a lever (not shown) to urge the valve head 19 away from the valve seat 18 to open the actuation valve 17.

Although in the above described embodiment the actuation valve 17 is disposed between the cartridge outlet 8A and the pressure relief valve 21 to selectively fluidly communicate the ouflet channel 14 therebctwccn, in an alternate embodiment (not shown) the pressure relief valve 21 may be disposed between the cartridge ouflet 8A and the actuation valve 1750 that the pressure reBef valve 21 remains open whilst the pressure in the formulation chamber 9 is greater than the pressure set-point and the formulation is fluidly communicated with the formulation outlet 6Awhen the actuation valve 17 is actuated.

In one embodiment, the cartridge 8 is received in the housing 2 and is removable therefrom by the user to refill or replace the cartridge 8. In an alternate embodiment, the cartridge is integray formed with the outer housing 2.

Referring to Figures 8 -10, an inhaler 101 according to a second embodiment of the invention is shown. The inhaler 101 maybe a nicotine delivery system that may be used as a substitute for cigarette, cigar or like smoking article. The inhaler 101 of the second embodiment of the invention is similar to the inhaler 1 of the first embodiment and comprises an outer housing 102 and an actuating mechanism 103. The outer housing Jo 102 comprises an eiIiptica cylinder shaped body 104 with a mouthpiece 105 at one end thereof having a formiflation ouflet io6A and a suction ouflet io6B therein.

The actuating mechanism 103 comprises an actuator 115 and an actuation valve 117.

The actuator 115 comprises a diaphragm ii6 that is pivotally mounted to an end of the i outer housing 102 that is dista' to the mouthpiece 105. The diaphragm n6 is disposed in an inner space 107 in the body 104 and partitions said space 107 into first and second compartments lo7A, 107Th The diaphragm ii6 seals the first compartment lo7A from the second compartment lo7B and a cartridge 108 is disposed in the first compartment 107A.

The cartridge 108 comprises a formulation chamber 109, a first plenum chamber iioA, and an intermediate chamber comprising a second plenum chamber noB. The formulation chamber 109 contains a formulation for inhalation that is pressurised so that it is above atmospheric pressure. The formulation chamber 109 is contained within an equalisation member comprising a flexible bag iii. The flexible bag iii comprises a sheet of impermeable material that is formed into a bag shape. The formulation chamber 109 in the bag 111 is fluidly communicated with a cartridge outlet io8A provided at an end of the cartridge 108.

The first plenum chamber nbA is disposed towards an end of the cartridge 108 that is remote of the cartridge ouflet io8A and the second plenum chamber loB is disposed between the formuthtion chamber 109 and the first plenum chamber iioA, on the outside of the bag 111 so that the impermeable material of the bag in seals the formulation chamber 109 from the second plenum chamber noB. The first and second plenum chambers iioA, noB are separated by a partitioning wall 112 and a passage 113 is formed therein to fluidly communicate the first plenum chamber iioA with the second plenum chamber noB.

As with the first embodiment of the invention, an outlet chann& 114 fluidly communicates the cartridge outlet io8A with the mouthpiece formulation outlet io6A.

The actuation valve 117 is configured to selectively block/unblock the outlet channel 114 so that formulation may be selectively supplied to the mouthpiece formulation outlet io6A from the formulation chamber 109 for inhalation by the user. The actuation valve 117 comprises a valve seat uS and a valve head 119. The valve seat uS is disposed in the io otiflet channd 114 and is configured to receive the va've head 119 to form a seal therebetween. The va've head 119 is mounted to the diaphragm n6 and rests against the valve seat n8 to block the outlet channel 114 when the actuation valve is in a closed position (as shown in Figure 9). The actuation valve 117 is moveable to an open position wherein the valve head 119 is urged away from the valve seat 118 so that the outlet channel 114 is unblocked (as shown in Figure to). A first biasing means 120, for example, a spring or portion of resilient material, is provided between the diaphragm 116 and the outer housing 102 to urge the diaphragm ii6 towards the longitudina' axis of the outer housing 102 so that the valve head 119 is urged towards the valve seat ii8 to bias the actuation valve 117 into the closed position.

The inside of the first compartment lo7A is sealed from the inside of the cartridge 108 and the outlet channel 114 and the inside of the second compartment lo7B is fluidly communicated with the end of the mouthpiece 105 by the suction outlet io6B.

Therefore, when the user sucks on the mouthpiece 105 to inhale formulation through the formulation outlet io6A, air in the second compartment lo7B is sucked through the suction outlet io6B so that the diaphragm ii6 pivots in a direction away from the longitudinal axis to open the actuation valve 117 in a similar manner to that described for the first embodiment of the invention.

As with the first embodiment of the invention, a pressure relief valve 121 is disposed in the ouflet channel 114, between the actuation valve 117 and the formulation outlet io6A, and is configured to permit the flow of formulation from the formulation chamber 109 to the formulation oufiet io6A when the pressure of the formulation in the outlet channel 114 on the formulation chamber 109 side of the pressure relief valve 121 reaches a pressure set-point, providing the actuation valve 117 is in its open position.

The first and second plenum chambers uoA, noB contain a pressurised liquid or gas.

The pressurised gas in the second plenum chamber iioB exerts a force on the exterior of the bag iii that urges the volume of the bag iii, and thus the volume of the formulation chamber 109, to decrease and therefore the pressure of the formation contained therein to increase. When the volume of the bag 111 decreases the volume of the second plenum chamber noB increases and therefore the pressure of the gas contained therein decreases. The volume of the bag iii will decrease under the force of the pressurised gas in the second plenum chamber noB until the pressure of the formulation in the formulation chamber 109 is equal to the pressure of the gas in the io second plenum chamber noB. Thus, the combined volume of the formulation and second plenum chambers 109, noB is fixed and the flexible bag 111 is configured to form a boundary therebetween that is moveable to adjust the relative volumes of the formulation and second plenum chambers 109, noB to equalise the prsures therein.

The second plenum chamber noB is fluidly communicated with the first plenum chamber iioA so that when the volume of the bag in is decreased and the pressure in the second plenum chamber noB decreases, gas will flow from the first plenum chamber iioA to the second plenum chamber iloB untfl the pressures therein are equal. Therefore, the flexible walls of the bag iii will deform until the volume of the formulation chamber 109 is such that the pressures in the formulation chamber 109 and the first and second plenum chambers irnA, noB are equal. The gas in the first and second plenum chambers iioA, iioB is pressurised to be above the pressure set-point required to open the pressure relief valve 121, and therefore the pressure of the formulation in the formulation chamber 109 will also be held at a pressure above the pressure set-point by the force of gas in the second plenum chamber iioB acting on the exterior walls of the bag in to compress the formulation contained therein.

In use, the user inhales to urge the diaphragm n6 away from the longitudinal axis of the outer housing 102 to open the actuation valve 117 and unblock the outlet channel 114 in the manner previous'y described, resulting in the inside of the formulation chamber 109 being fluidly communicated with the pressure rehef valve 121. As the pressure of the formulation in the formulation chamber 109 is initially above the pressure set-point, the pressure rehef valve 121 will open and forniulation will flow through the ouflet channel 114 to be expelled out of the formulation outlet io6A of the mouthpiece 105 for inhalation by the user. When formulation is expelled from the formulation chamber 109, the pressure therein will decrease and volume of the bag iii will decrease under the force of the pressure of the gas in the second plenum chamber -22-noB acting on the exterior walls of the bag 111, until the pressures in the formulation chamber 109 and second plenum chamber noB equalise. The volume of the bag iii will continue to decrease and formdation will continue to be expelled out of the formulation chamber 109 until the equallsed pressure in the formidation chamber 109 and second plenum chamber noB is less than the pressure set-point required to open the pressure relief valve 121, at which point the pressure relief valve 121 will close.

When the volume of the flexible bag 111 is decreased in response to the release of formulation from the formulation chamber 109, pressurised gas in the first plenum io chamber noA flows through the passage 113 and into the second plenum chamber iloB to increase the pressure therein until the pressures in the first and second plenum chambers iioA, noB are equalised. This will cause the pressure in the second plenum chamber noB to exert a force on the exterior of the bag 111 to decrease the volume of the formulation chamber 109 until the pressures in the formulation chamber 109 and the first and second p'enum chambers iioA, noB are all equallsed and are above the pressure set-point. The user may then again inha'e to reopen the actuation va've 117, resulting in the pressure of the formiflation in the formulation chamber 109 opening the pressure relief valve 121 and formulation being expelled out of the formulation outlet io6A of the mouthpiece 105 for inhalation by the user. Formulation will continue to be expelled from the formulation chamber 109 until the pressure therein is less than the pressure set-point required to open the pressure relief valve 121, at which point the pressure relief valve 121 will close. As formulation is only released from the formulation chamber 109 whilst the pressure therein is above the pressure set-point, each inhalation by the user will result in an incremental reduction of the volume of the flexible bag in and therefore a metered dosage of formulation being expelled from the inhaler 101. The restored pressure upon equalisation in the formulation chamber and in the first and second plenum chambers will be less after each release of formulation from the formulation chamber. The process of releasing dosages of formulation may be repeated until no formulation remains in the formuaflon chamber 109 or the pressure in the first and second plenum chambers nbA, noB is less than the pressure set-point required to open the pressure rellef valve 121.

As described in reference to the first embodiment of the invention, the passage 113 has a small diameter so that is has a large flow resistance, resulting in a low flow rate of the pressurised gas flowing between the first and second plenum chambers noA, noB during equalisation thereof. Therefore, when the pressure in the second plenum -23 -chamber noB is less than the pressure set-point of the pressure relief valve 121 due to the release of formulation from the formulation chamber 109, the gas in the first pernim chamber nbA will flow into the second pkrnim chamber iioB gradually. Thus, it will take a certain period of time for the gas in the first p'enum chamber noA to flow into the second plenum chamber noB via the passage 113 to re-pressurise the second plenum chamber noB to a pressure greater than the pressure set-point of the pressure relief valve 121 and so, after inhalation of the formulation, the user must wait said period of time before the actuation valve 117 may again be opened to release another dosage of formulation for inhalation. This means that the inhaler 101 has the advantage io of releasing metered dosage of formulation with a time dethy between successive dosages to ensure that the user may not consume more than a pre-determined amount of formulation within a certain time period.

Although in the above described embodiment the equalisation member comprises a flexible bag iii of impermeable material that contains the formulation chamber 109, in an alternate embodiment (not shown), the equallsation member comprises a portion of flexible impermeable material that forms a dividing wall between the formdation chamber 109 and the second plenum chamber noB. In such an embodiment, the dividing wall deforms to adjust the size of the formulation chamber 109 relative to the second plenum chamber noB to equalise the pressures therein.

Although in the above described embodiment the flexible bag iii contains the formulation chamber 109 and the second plenum chamber noB is disposed around the exterior of the bag in, in an alternate embodiment (not shown) the flexible bag iii contains the second plenum chamber noB and the formulation chamber 109 is disposed around the exterior of the bag iii. In such an embodiment, the pressure of the gas in the second plenum chamber noB exerts a force on the interior wall of the flexible bag iii to pressurise the formulation on the outside thereof. In one such embodiment, the first plenum chamber noA may also be provided in the flexible bag in and separated from the second plenum chamber noB by a constriction provided in the flexible bag in. The constriction may be achieved, for example, by threading the bag through the passage 113 in the partitioning wall 112 prior to inflating the bag with the pressurised fluid or by positioning a loop of material around the outside of the bag and then tightening said loop. The constriction acts as a passage having a large flow resistance so that fluid flows from the first plenum chamber noA to the second plenum chamber noB at a low flow rate to equalise the pressures therein. In yet another -24 -embodiment, a flexible bag 111 is provided to contain the formulation chamber 109 and a second flexible bag is provided to contain the second plenum chamber noB.

Referring to Figures 11 -14, an inhaler 201 according to a third embodiment of the invention is shown. The inhaler 201 may be a nicotine delivery system that may be used as a substitute for cigarette, cigar or like smoking article. The inhaler 201 comprises an outer housing 202 and an actuating mechanism 203. The outer housing 202 comprises an elliptical cylinder shaped body 204 with a mouthpiece 205 at one end thereof having a formulation outlet 2o6A and a suction outlet 2o6B therein. I0

An inner space 207 is formed in the body 204 and has a cartridge 208 disposed therein.

As with the second embodiment of the invention, the cartridge 208 comprises a formulation chamber 209, a first plenum chamber 2loA, and an intermediate chamber comprising a second plenum chamber 210B. The formulation chamber 209 contains a formulation for inhalation that is pressurised so that it is above atmospheric pressure.

The formulation chamber 209 is contained within an equalisation member comprising a flexible bag 211. The flexible bag 211 comprises a sheet of impermeabk material that is formed into a bag shape. The formulation chamber 209 in the bag 211 is fluidly communicated with a cartridge outlet 208A provided at an end of the cartridge 208.

The first plenum chamber 210A is disposed towards an end of the cartridge 208 that is remote of the cartridge outlet 208A and the second plenum chamber 210B is disposed between the formulation chamber 209 and the first plenum chamber 210A, on the outside of the bag 211 so that the impermeable material of the bag 211 seals the formulation chamber 209 from the second plenum chamber 21DB. The first and second plenum chambers 2loA, 210B are separated by a partitioning wall 212 and a passage 213 is formed therein to fluidly communicate the first plenum chamber 210A with the second plenum chamber 2loB.

The actuating mechanism 203 comprises a pressure relief valve 216 having a valve housing 217, valve seat 218, valve head 219 and a first biasing means 220. The valve housing 217 comprises a peripheral wall 217A that encloses a valve chamber 217B. An ouflet chann& 221 is provided in the peripheral wall of the valve housing 217 and fluidly communicates the valve chamber 217B with the formulation outlet 206A of the mouthpiece 205. The cartridge outlet 208A is disposed at one end of the valve chamber 217B and the suction outlet 206B is disposed towards the other end thereof. A valve -25 -head 219 comprising a piston is slidably received in the valve chamber 217B. The valve head 219 comprises a valve face 219A that faces in a direction towards the valve seat 218. The valve seat 218 is disposed around the cartridge ouflet 208A and is configured to receive the valve face 219A.

The pressure relief valve 216 is moveable between first, second and third positions. In the first position, the valve head 219 is disposed at an end of the valve chamber 217B that is proximate to the cartridge outlet 208A so that the valve face 219A sits flush to the valve seat 218 and only a portion of the surface area of the valve face 219A is fluidly io communicated with the cartridge ouflet 208A (as shown in Figure 12). The first biasing means 220 urges the valve head 219 towards the valve seat 218 and therefore biases the pressure relief valve 216 into the first position. The cross-sectional surface area of the cartridge outlet 2o8A is small relative to the surface area of the valve face 219A and so the pressure of the formulation contained in the formulation chamber 209 only exerts a force over a small surface area of the valve face 219A when the valve head 219 abuts the valve seat 218. This force is insufficient to overcome the biasing force of the biasing means 220 to urge the valve head 219 away from the valve seat 218. When the pressure relief valve 216 is in the first position, the valve head 219 blocks the outlet channel 221 from the cartridge outlet 208A to prevent formulation from flowing from the formulation chamber 209 to the formulation outlet 2o6A of the mouthpiece 205.

When the user sucks on the mouthpiece 205 to inhale formulation through the formulation outlet 206A, air is drawn through the suction outlet 206B and the pressure in the valve chamber 217B on the opposite side of the valve head 219 to the cartridge outlet 2o8A reduces, causing a force to be exerted on the valve head 219 that is sufficient to overcome the biasing force of the first biasing means 220 so that the valve head 219 is urged away form the valve seat 218 and the pressure relief valve 216 moves into the second position (as shown in Figure 13). When the pressure relief valve 216 is in the second position, the outkt channel 221 remains sealed from the cartridge ouflet 208A by the valve head 219.

With the pressure rehef valve 216 moved into the second position so that the valve head 219 is urged away from the valve seat 218, the entire surface area of the valve face 219A is exposed to the pressure of the formulation in the cartridge outlet 2o8A. As the pressure of the formulation now acts on a greater surface area of the valve face 219A, a greater force is exerted on the valve head 219. Therefore, when the pressure relief valve -26 - 216 is in the second position and the pressure of the formulation in the formulation chamber 209 is above a pressure set-point, the force acting on the valve head 219 will be sufficient to slide the valve head 219 further away from the valve seat 218 and into a third position (as shown in Figure 14). When the pressure relief va've 216 moves into the third position, the valve head 219 passes the outlet channel 221 so that the outlet channel 221 is fluidly communicated with the cartridge outlet 208A and thus formulation may be expelled from the formulation outlet 2o6A.

The first and second plenum chambers 2loA, 2loB contain a pressurised liquid or gas.

io The pressurised gas in the second plenum chamber 210B exerts a force on the exterior of the bag 211 that urges the volume of the bag 211, and thus the volume of the formulation chamber 209, to decrease and therefore the pressure of the formation contained therein to increase. When the volume of the bag 211 decreases the volume of the second plenum chamber 2loB increases and therefore the pressure of the gas contained therein decreases. The volume of the bag 211 will decrease under the force of the pressurised gas in the second plenum chamber 210B until the pressure of the formulation in the formulation chamber 209 is equal to the pressure of the gas in the second plenum chamber 210B. Thus, the combined volume of the formulation and second plenum chambers 209, 210B is fixed and the flexible bag 211 is configured to form a boundary therebetween that is moveable to adjust the relative volumes of the formulation and second plenum chambers 209, 2loB to equalise the pressures therein.

The second plenum chamber 210B is fluidly communicated with the first plenum chamber 210A so that when the volume of the bag 211 is decreased and the pressure in the second plenum chamber 210B decreases, gas will flow from the first plenum chamber 210A to the second plenum chamber 2mB until the pressures therein are equal. Therefore, the flexible walls of the bag 211 will deform until the volume of the formulation chamber 209 is such that the pressures in the formulation chamber 209 and the first and second plenum chambers 2loA, 2mB are equal. The gas in the first and second plenum chambers 210A, 210B is pressurised to be above the pressure set-point reqtured to urge the pressure rebef valve 216 from the second position to the third position, and therefore the pressure of the formuktion in the formulation chamber 209 will also be h&d at a pressure above the pressure set-point by the force of gas in the second plenum chamber 210B acting on the exterior walls of the bag 211 to compress the formulation contained therein. -27-

In use, the user inhales to urge the valve head 219 away form the valve seat 218 so that the pressure relief valve 216 moves into the second position in the manner previously described, resifiting in the entire valve face 219A being fluidly communicated with the formulation in the formulation chamber 209. As the pressure of the formulation in the formulation chamber 209 is initially above the pressure set-point, the pressure of the formulation acting on the valve face 219A will overcome the force of the first biasing means 220 to urge the valve head 219 further away from the valve seat 218 so that the pressure relief valve 216 moves into the third position. When the pressure relief valve 216 is in the third position the formulation chamber 209 is fluidly communicated with io the mouthpiece formulation ouflet 2o6A, via the ouflet channel 221, and so formulation will be expelled out of the formuthtion ouflet 2o6A for inhalation by the user. In a similar manner to the second embodiment of the invention, when formulation is expelled from the formulation chamber 209 the pressure therein will decrease and so the volume of the bag 211 will decrease under the force of the pressure of the gas in the second plenum chamber 210B acting on the exterior walls of the bag 211, until the pressures in the formuthtion chamber 209 and second plenum chamber 210B equalise.

The volume of the bag 211 will continue to decrease and formiflation will continue to be expelled out from the formulation chamber 209 until the equalised pressure in the formulation chamber 209 and second plenum chamber 210B is less than the pressure set-point required to overcome the biasing force of the biasing means 220 to urge the actuation valve into the third position, at which point the pressure relief valve 216 will move back to the second position and the cartridge outlet 208A will be sealed from the outlet channel 221 by the valve head 219. If the user then stops inhaling, the pressure relief valve 216 will move back to the first position.

When the flexible bag 211 is decreased in volume in response to the release of formulation from the formulation chamber 209, pressurised gas in the first plenum chamber 210A flows through the passage 213 and into the second plenum chamber 2loB to incrcase the pressure therein until the pressures in thc first and second plcnum chambers 2loA, 210B are equalised. This will cause the pressure in the second plenum chamber 210B to exert a force on the exterior of the bag 211 to decrease the volume of the formulation chamber 209 until the pressures in the formulation chamber 209 and the first and second p'enum chambers 2loA, 210B are all equabsed and are at a pressure above the pressure set-point required to urge the pressure relief valve 216 from the second position to the third position. The user may then again inhale to move the pressure relief valve 216 into the second position so that the entire valve face 219A is fluidly communicated with the formulation chamber 209 and the formulation exerts a force on the valve face 219A to urge the pressure relief valve 216 into the third position so that formulation is again expelled from the formulation outkt 2o6A for inhalation by the user. Formdation wifi continue to be expelled from the formulation chamber 209 until the pressure therein is less than the pressure set-point required to urge the pressure relief valve 216 into the third position, at which point the pressure relief valve 216 will move back to the second position and the cartridge outlet 208A will be sealed from the outlet channel 221 by the valve head 219. As formulation is only released from the formulation chamber 209 whilst the pressure therein is above the io pressure set-point, each inhalation by the user will resut in an incremental reduction of the vohime of the flexible bag 211 and therefore a metered dosage of formdation being expelled from the inhaler 201. The process of releasing dosages of formulation may be repeated until no formulation remains in the formulation chamber 209 or the pressure in the first and second plenum chambers 2loA, 2loB is less than the pressure set-point.

As described in reference to the second embodiment of the invention, the passage 213 has a small diameter so that is has a large flow resistance, resifiting in a low flow rate of the pressurised gas flowing between the first and second plenum chambers 210A, 210B during equalisation thereof. Therefore, when the pressure in the second plenum chamber 210B is less than the pressure set-point required to urge the pressure relief valve into the third position, the gas in the first plenum chamber 210A will flow into the second plenum chamber 210B gradually. Thus, it will take a certain period of time for the gas in the first plenum chamber 210A to flow into the second plenum chamber 210B via the passage 213 to re-pressurise the second plenum chamber 210B to a pressure greater than the pressure set-point and so, after inhalation of the formulation, the user must wait said period of time before the pressure relief valve 216 may again be moved into the third position to release another dosage of formulation for inhalation.

This means that the inhaler 201 has the advantage of reieasing metered dosage of formulation with a time dethy between successive dosages to ensure that the user may not consume more than a pre-determined amount of formulation within a certain time period. Furthermore, the strength of the first biasing means 220 is s&ected so that the biasing force it exerts on the valve head 219 to urge the pressure rehef valve 216 from the third position to the second position is greater than the force exerted on the valve head 219 as a result of inhalation by the user. Therefore, when the user inhales and the pressure of the formulation is below the pressure set-point, the force exerted on the -29 -valve head 219 by the pressure drop in the valve chamber 217B created by the user will only ever be sufficient to move the valve into the second position, rather than the third position, and so formulation will not be released until the second plenum chamber 2loB re-pressurises to exert a force on the flexible bag 211 to pressurise the formulation in the formulation chamber 209 to above the pressure set-point.

Although in the above described embodiment the equalisation member comprises a flexible bag 211, in an alternate embodiment (not shown) the equalisation member may be of a similar construction to that described in the first embodiment of the invention, io comprising a piston that is sBdably received within cartridge and seals the formulation chamber from the second plenum chamber.

A fourth embodiment of the present invention is shown in Figures 15 -17 and is generally the same as the third embodiment shown in Figures 11 -14. As with the third embodiment of the invention, the inhaler of the fourth embodiment comprises a cartridge 308 having a formuthtion chamber 309, a first plenum chamber (not shown) and an intermediate chamber comprising a second plenum chamber (not shown). A difference between the inhaler 201 of the third embodiment of the invention and the inhaler of the fourth embodiment is that the actuating mechanism 203 of the inhaler 201 of the third embodiment is omitted and is replaced by an alternative actuating mechanism 303.

The actuating mechanism 303 of the inhaler of the fourth embodiment of the invention comprises a pressure relief valve 316 having a valve housing 317, valve seat 318, valve head 319 and a first biasing means 320. The valve housing 317 comprises a peripheral wall 317A that encloses a valve chamber 317B. A cartridge outlet 308A is disposed at one end of the valve chamber 317B and a suction outlet 3o6A is disposed at the other end thereof. The valve chamber 317B comprises a section of decreased diameter 317C that is proximate to the cartridge outlet 3oSA and a section of increased diameter 317D o that is distal to the cartridge outlet 3o8A. A valve head 319 is slidably received in the valve chamber 317B. The valve head 319 comprises a valve face 319A that faces in a direction towards the valve seat 318. The valve seat 318 is disposed around the cartridge outlet 308A at the end of the valve chamber 317B of decreased diameter 317C and is configured to receive the valve face 319A.

The pressure relief valve 316 is moveable between first, second and third positions. In the first position, the valve head 319 is disposed in the section of the valve chamber 317B of decreased diameter 317C so that the valve face 319A sits flush to the valve seat 318 and only a portion of the surface area of the valve face 319A is fluiffly communicated with the cartridge outlet 308A (as shown in Figure 15). The first biasing means 320 urges the valve head 319 towards the valve seat 318 and therefore biases the pressure relief valve 316 into the first position. The cross-sectional surface area of the cartridge outlet 308A is small relative to the surface area of the valve face 319A and so the pressure of the formulation contained in the formulation chamber 309 only exerts a io force over a small surface area of the valve face 319A when the valve head 319 abuts the valve seat 318. This force is insufficient to overcome the biasing force of the biasing means 320 to urge the valve head 319 away from the valve seat 318. When the pressure relief valve 316 is in the first position, the valve face 319A blocks the outlet channel 321 from the cartridge outlet 3o8A to prevent formulation from flowing from the formulation chamber 309 to the suction outlet 3o6A for inhalation by the user.

When the user appbes suction to the suction outlet 3o6A, air is dram through the suction outlet 306A and the pressure in the valve chamber 317B on the opposite side of the valve head 319 to the cartridge outlet 308A reduces, causing a force to be exerted on the valve head 319 that is sufficient to overcome the biasing force of the first biasing means 320 so that the valve head 319 is urged away form the valve seat 318 and the pressure relief valve 316 moves into the second position (as shown in Figure 16). When the pressure relief valve 316 is in the second position, the valve head 319 is still disposed in the section of the valve chamber 317B of reduced diameter 317C. The valve head 319 is sealed against the peripheral wall of the valve housing 317 when the valve head 319 is disposed in the section of the valve chamber 317B of reduced diameter 317C and therefore when the valve head is in the first and second positions the valve head 319 seals the cartridge outlet 3o8A from the suction outlet 3O6Aso that no formulation may be released therefrom.

With the pressure rebef valve 316 moved into the second position so that the valve head 319 is urged away from the valve seat 318, the entire surface area of the valve face 319A is exposed to the pressure of the formu'ation in the cartridge ouflet 3o8A. As the pressure of the formulation now acts on a greater surface area of the valve face 319A, a greater force is exerted on the valve head 319. Therefore, when the pressure relief valve 316 is in the second position and the pressure of the formulation in the formulation chamber 309 is above a pressure set-point, the force acting on the valve head 319 will be sufficient to slide the valve head 319 further away from the valve seat 318 and into a third position (as shown in Figure 17). When the pressure relief valve 316 moves into the third position, the valve head 319 is disposed in the section of the valve chamber 317B of increased diameter 317D and so a gap is formed between the valve head 319 and the peripheral wall 317A of the valve housing 317. The gap forms an outlet channel 321 that fluidly communicates the cartridge outlet 3o8A with the suction outlet 306A so that formulation may expelled from the suction outlet 3o6A for inhalation by the user.

io When the pressure relief valve 316 is urged into the third position and formulation is released from the formulation chamber for inhalation, the pressure of the formulation contained therein will decrease until it is less than the pressure set-point, at which point the pressure relief valve 316 will move back into the second position. As described above in relation to the third embodiment of the invention, the cartridge 308 comprises a passage (not shown) that fluidly communicates the first and second plenum chambers and has a restricted flow rate such that there is a dday in the time it takes for the formulation chamber to be re-pressurised after r&ease of formulation for inhalation by the user. Therefore the user must wait for the formulation chamber to re-pressurise before the pressure acting on the valve head 319 is sufficient to overcome the first biasing means 320 and move the pressure relief valve 316 into the third position again for the release of another dosage of formulation from the formulation chamber 309 for inhalation. Therefore, a metered dosage of formulation is expelled from the inhaler upon inhalation by the user and the user must wait a period of time before a subsequent dosage of formulation may be administered.

A fifth embodiment of the present invention is shown in Figures i8 -20 and is generally the same as the third embodiment shown in Figures 11 -14. As with the third embodiment of the invention, the inhaler of the fifth embodiment comprises a cartridge 408 having a formu'ation chamber 409, a first plenum chamber (not shown), and an intermediate chamber comprising a second plenum chamber (not shown). A difference between the inhaler 201 of the third embodiment of the invention and the inhaler of the fifth embodiment is that the actuating mechanism 203 of the inhaler 201 of the third embodiment is omitted and is replaced by an ahemative actuating mechanism 403.

The actuating mechanism 403 of the inhaler of the fifth embodiment of the invention comprises a pressure relief valve 416 having a valve housing 417, a valve head 419 and a first biasing means 420. The valve housing 417 comprises a peripheral wall 417A that encloses a valve chamber 417B. A cartridge outlet 408A is disposed at one end of the valve chamber 417B and a suction ouflet 4o6B is disposed towards the other end thereof. The valve chamber 417B comprises a decreased diameter section 417C that is proximate to the cartridge outlet 4o8A and a increased diameter section 417D that is distal to the cartridge outlet 408A. An outlet channel 421 is provided in the peripheral wall 417A at the increased diameter section 417D of the valve chamber 417B and fluidly communicates the valve chamber 417B with a formulation outlet 4o6A that is provided in a mouthpiece 405 of the inhaler. The valve head 419 is slidably received in the valve io chamber 417B and comprises a first va've portion 419A having a reduced diameter and a second valve portion 419B having an increased diameter. The first and second valve portions 419A, 419B comprise first and second valve faces 419C, 419D respectively. The first and second valve faces 419C, 419D each face towards the cartridge outlet 4o8A.

The pressure relief valve 416 is moveable between first, second and third positions. In the first position, the first valve portion 4l9Ais disposed in the decreased diameter section 417C of the valve chamber 417B so that the peripheral wafi of the first valve portion 419A abuts the inside of the peripheral wall 417A of the decreased diameter section 417C of the valve chamber 417B so that only the first valve face 419C is fluidly communicated with the cartridge outlet 408A (as shown in Figure i8). The first biasing means 420 urges the valve head 419 towards the cartridge outlet 408A and therefore biases the pressure relief valve 416 into the first position. The surface area of the first valve face 419C is small enough that the pressure of the formulation contained in the formulation chamber 409 is only exposed to a small portion of the total surface area of the valve head 419 when the pressure relief valve 416 is in the first position and so the force exerted on the valve head 419 by the pressure of the formulation at the cartridge outlet 408A is relatively small. This force is insufficient to overcome the biasing force of the biasing means 420 to move the valve head 419 relative to the valve housing 417.

When the pressure relief v&vc 416 is in the first position, the valve head 419 blocks the outlet channd 421 from the cartridge outlet 4o8Ato prevent formulation from flowing from the formifiation chamber 409 to the formulation outlet 406A for inhalation by the user.

When the user applies suction to the suction outlet 406B, air is drain through the suction outlet 4o6B and the pressure in the valve chamber 417B on the opposite side of the valve head 419 to the cartridge outlet 4o8A reduces, causing a force to be exerted on the valve head 419 that is sufficient to overcome the biasing force of the first biasing means 420 so that the valve head 419 is urged away from the cartridge outlet 408A and the pressure relief valve 416 moves into the second position (as shown in Figure 19).

When the pressure relief valve 416 is in the second position, the first and second valve portions 419A, 419B are both disposed in the increased diameter section 417D of the valve chamber 417B and so the peripheral wall of the first valve portion 419A no longer seals against the inside of the peripheral wall 417A of the decreased diameter section 417C of the valve chamber 417B. The peripheral wall of the second valve portion 419B seals against the inside of the peripheral wall 417A of the increased diameter section Jo 417D of the valve chamber 417B when the pressure relief valve 416 is in the second position, and so the valve head 419 b'ocks the outlet channd 421 from the cartridge outlet 4o8A to prevent formulation from flowing from the formulation chamber 409 to the formulation outlet 4o6A for inhalation by the user.

When the pressure relief valve 416 is moved into the second position, the second valve face 419D is fluidly communicated with the cartridge outlet 4o8A. As the pressure of the formulation at the cartridge outlet 4o8A now acts on both the first and second valve faces 419C, 419D, a greater surface area of the valve head 419 is exposed to the pressure of the formulation at the cartridge outlet 4o8A than when the pressure relief valve 416 is in the first position and so a greater force is exerted on the valve head 419. Therefore, when the pressure relief valve 416 is in the second position and the pressure of the formulation in the formulation chamber 409 is above a pressure set-point, the force acting on the valve head 419 will be sufficient to overcome the force of the biasing means 420 and slide the valve head 419 further away from the cartridge outlet 408A and into the third position (as shown in Figure 20). When the pressure relief valve 416 moves into the third position, the second valve portion 419B of the valve head 419 passes the outlet channel 421 so that the outlet channel 421 is fluidly communicated with the cartridge outlet 4oSA, via a gap between the first valve portion 419A and the peripheral wall 417A of thc incrcased diameter section 417D of the valve chamber 417B, and thus formulation may be expefled from the formulation outlet 4o6A for inhalation by the user.

When the pressure relief valve 416 is urged into the third position and formulation is released from the formulation chamber 409 for inhalation, the pressure of the formulation contained therein will decrease until it is less than the pressure set-point, at which point the pressure relief valve 416 will move back into the second position. As described above in relation to the third embodiment of the invention, the cartridge 408 comprises a passage (not shown) that fluidly communicates the first and second pernim chambers and has a restricted flow rate such that there is a delay in the time it takes for the formulation chamber to be re-pressurised after release of formiflation for inhalation by the user. Therefore the user must wait for the formulation chamber to re-pressurise before the pressure acting on the valve head 419 is sufficient to overcome the first biasing means 420 and move the pressure relief valve 416 into the third position again for the release of another dosage of formulation from the formulation chamber 409 for inhalation. Therefore, a metered dosage of formulation is expelled from the io inhaler upon inhalation by the user and the user must wait a period of time before a subsequent dosage of formulation may be administered.

Referring to Figures 21 and 22, an inhaler 501 according to a sixth embodiment of the invention is shown. The inhaler 501 may be a nicotine delivery system that may be used as a substitute for cigarette, cigar or Uke smoking article. The inhaler 501 of the sixth embodiment of the invention is similar to the inhaler lot of the second embodiment and comprises an outer housing 502 and an actuating mechanism 503. The outer housing 502 comprises an elliptical cylinder shaped body 504 with a mouthpiece 505 at one end thereof having a formulation outlet 5o6A and a suction outlet o6B therein.

The actuating mechanism 503 comprises an actuator 515 and an actuation valve 517.

The actuator 515 comprises a diaphragm i6 that is pivotally mounted to an end of the outer housing 502 that is distal to the mouthpiece 505. The diaphragm i6 is disposed in an inner space 507 in the body 504 and partitions said space 507 into first and second compartments 507A, 5o7B. The diaphragm i6 seals the first compartment 5o7A from the second compartment 5o7B and a cartridge o8 is disposed in the first compartment 5o7A.

The cartridge 508 comprises a formulation chamber 509, a first plenum chamber ioA and an intermediate chamber ioB. The formulation chamber 509 and the intermediate chamber ioB contain a formulation for inhalation. The formulation chamber 509 and intermediate chamber ioB are contained within an equalisation member comprising a flexible bag 5n. The flexible bag 511 comprises a sheet of impermeable material that is formed into a bag shape. The formulation chamber 509 in the bag 511 is fluidly communicated with a cartridge outlet o8A provided at an end of the cartridge so8.

The first plenum chamber 5ioA is disposed towards an end of the cartridge 508 that is remote of the cartridge ouflet o8A, on the outside of the bag 511 50 that the impermeable materia' of the bag 511 se&s the inside of the bag ii, and thus the intermediate chamber 5ioB and the formulation chamber 509, from the first plenum chamber 5ioA. A wall 512 is provided in the cartridge o8 and comprises an aperture therethrough 513. The bag 511 is disposed within the cartridge o8 such that it passes through the aperture 513 in the wall 512, with the formulation chamber 509 on one side of the wall 512, proximate to the cartridge outlet 5o8A, and the intermediate chamber o 5loB on the other side of the wall 512, remote of the cartridge outlet 508A. The aperture 513 in the wall 512 acts as a constriction on the bag u that forms a passage 513A that fluidly communicates the formulation chamber 509 with the intermediate chamber 510B. The wall 512 seals the first plenum chamber 5ioA from the portion of the exterior of the bag 511 that forms the formulation chamber 509. The exterior of the is portion of the bag 511 that forms the formulation chamber 509 is provided in a fourth chamber ioC that contains a fluid that is pressurised to above atmospheric pressure.

The fourth chamber ioC is sealed from the formulation chamber 509 by the flexible bag 511 and is sealed from the first plenum chamber 5ioA by the wall 512.

In an alternative embodiment (not shown) the constriction is formed by positioning a loop of material around the outside of the bag 511 and then tightening said loop. In yet another embodiment, the bag 511 itself is constructed so that it is an hourglass' shape so that the bag 511 has a narrowed portion that forms the constriction between the formulation chamber 509 and the intermediate chamber 510B.

As with the first embodiment of the invention, an outlet channel 514 fluidly communicates the cartridge outlet o8A with the mouthpiece formulation outlet so6A.

The actuation valve 517 is configured to selectively block/unblock the outlet channel 514 so that formulation may bc sclcctivcly supplied to the mouthpiece formifiation outlet 5o6A from the formulation chamber 509 for inhalation by the user. The actuation valve 517 comprises a valve seat i8 and a valve head 519. The valve seat i8 is disposed in the outlet channel 514 and is configured to receive the valve head 519 to form a seal therebetween. The valve head 519 is mounted to the diaphragm i6 and rests against the valve seat s18 to block the outlet channel 514 when the actuation valve 517 is in a closed position (as shown in Figure 21). The actuation valve 517 is moveable to an open position wherein the valve head 519 is urged away from the valve seat si8 so that the outlet channel 514 is unblocked (as shown in Figure 22). A first biasing means 520, for example, a spring or portion of resilient material, is provided between the diaphragm i6 and the outer housing 502 to urge the diaphragm i6 towards the longitudinal axis of the outer housing 502 so that the va've head 519 is urged towards the valve seat i8 to bias the actuation valve 517 into the closed position.

The inside of the first compartment 5o7A is sealed from the inside of the cartridge o8 and the outlet channel 514 and the inside of the second compartment 5o7B is fluidly communicated with the end of the mouthpiece 505 by the suction outlet 5o6B.

io Therefore, when the user sucks on the mouthpiece 505 to inhale formtilation through the formulation outlet o6A, air in the second compartment 5o7B is sucked through the suction outlet o6B so that the diaphragm 516 pivots in a direction away from the longitudinal axis to open the actuation valve 517 in a similar manner to that described for the first embodiment of the invention.

As with the first embodiment of the invention, a pressure relief valve 521 is disposed in the ouflet channel 514, between the actuation valve 517 and the formulation ouflet 5o6A, and is configured to permit the flow of formulation from the formulation chamber 509 to the formulation outlet o6A when the pressure of the formulation in the outlet channel 514 on the formulation chamber 509 side of the pressure relief valve 521 reaches a pressure set-point, providing the actuation valve 517 is in its open position.

The first plenum chamber 5ioA contains a pressurised liquid or gas. The pressurised gas in the first plenum chamber 5ioA exerts a force on the exterior of the portion of the bag 511 that forms the intermediate chamber ioB to urge the volume of said portion of the bag 511, and thus the volume of the intermediate chamber 509, to decrease and therefore the pressure of the formation contained therein to increase to the same pressure as the pressurised fluid contained in the first plenum chamber 510A. When o the vohime of the portion of the bag n that forms the intermediate chamber 5loB decreases, the volume of the first plenum chamber ioA increases and therefore the pressure of the gas contained therein decreases. Thus, the combined volume of the first p'enum chamber ioA and intermediate chamber ioB is fixed and the flexible bag ii is configured to form a boundary therebetween that is moveable to adjust the relative volumes of the first plenum chamber 5ioA and the intermediate chamber 5ioB to equalise the pressures therein. Therefore, the flexible walls of the bag 511 will deform until the volume of the intermediate chamber 5ioB is such that the pressures in the intermediate chamber 510B and the first plenum chamber 5ioA are equal. The intermediate chamber ioB is fluidly communicated wIth the formifiation chamber 509, via the passage 513A, so that when formulation is released from the formiflation chamber 509 and the pressure in the formulation chamber 509 decreases, formulation will flow from the intermediate chamber 5ioB to the formulation chamber 509 until the pressures therein are equal. As formulation flows into the formulation chamber 509 50 that its volume increases, the volume of the fourth chamber ioC will decrease and therefore the pressure of the gas contained therein, which acts on the exterior of the Jo portion of the bag 511 that forms the formtilation chamber 509, will increase, which will result in an increased force being exerted on said portion of the bag n. Therefore, the formulation chamber 509 will remain pressurised when the volume of the portion of the bag 511 that forms the formulation chamber 509 expands as formulation flows thereto from the intermediate chamber 510B. In an alternate embodiment, the formulation chamber 509 is kept pressurised as the vohime of the portion of the bag 511 that forms the formifiation chamber 509 expands by manufacturing said portion from a resilient material, for example, thtex or porurethane, that is stretched as said portion of the bag 511 expands.

Formulation will flow between the intermediate chamber 5ioB and the formulation chamber 509 until the pressures in the formulation chamber 509, first plenum chamber 5ioA, intermediate chamber 5ioB and the fourth chamber ioC are all equalised. The gas in the first plenum chamber 5ioA is pressurised to be above the pressure set-point required to open the pressure relief valve 521, and therefore the pressure of the formulation in the formulation chamber 509 will also be held at a pressure above the pressure set-point by the force of gas in the first plenum chamber iioA acting on the exterior walls of the bag 511 to compress the formulation contained in the intermediate chamber ioB, which is fluidly communicated with the formulation chamber 509 by the passage 513A. 3°

In use, the user inhales to urge the diaphragm i6 away from the longitudinal axis of the outer housing 502 to open the actuation valve 517 and unblock the outkt channel 514 in the manner previously described, resulting in the inside of the forniiilation chamber 509 being fluidly communicated with the pressure relief valve 521. As the pressure of the formulation in the formulation chamber 509 is initially above the pressure set-point, the pressure relief valve 521 will open and formulation will flow through the outlet channel 514 to be expelled out of the formulation outlet o6A of the mouthpiece 505 for inhalation by the user. When formulation is expelled from the formulation chamber 509, the pressure therein will decrease, until afi of the formulation contained in the formulation chamber 509 is exp&led therefrom or the pressure in the formulation chamber 509 is less than the pressure set-point required to open the pressure relief valve 521, at which point the pressure relief valve 521 will close.

When the pressure in the formulation chamber 509 is decreased to below the pressure set-point in response to the release of formulation from the formulation chamber 509, Jo pressurised gas in the intermediate chamber 5ioB flows through the passage 513A and into the formulation chamber 509, under the force of the pressurised gas in the first plenum chamber ioA acting on the exterior of the portion of the bag 511 that forms the intermediate chamber 5ioB, to increase the pressure in the formulation chamber 509 until the pressures in the formulation chamber 509, first plenum chamber 5ioA and intermediate chamber 5ioB are afi equaBsed and are above the pressure set-point. The user may then again inhale to reopen the actuation valve 517, resulting in the pressure of the formulation in the formulation chamber 509 opening the pressure reflef valve 521 and formulation being expelled out of the formulation outlet o6A of the mouthpiece 505 for inhalation by the user. Formulation will continue to be expelled from the formulation chamber 509 until all of the formulation contained in the formulation chamber 509 is expelled therefrom or the pressure in the formulation chamber 509 is less than the pressure set-point required to open the pressure relief valve 521, at which point the pressure relief valve 521 will close. As formulation is only released from the formulation chamber 509 whilst the pressure therein is above the pressure set-point, each inhalation by the user will result in an incremental reduction of the amount of formulation contained in the flexible bag sit and therefore a metered dosage of formulation being expelled from the inhaler 501. The restored pressure upon equalisation in the formulation chamber 509, first plenum chamber 5loA and intermediate chamber 5ioB will be css after cach rclcasc of formulation from the formulation chamber 509. The process of releasing dosages of formulation may be repeated until no formuthtion remains in the formulation chamber 509 and the intermediate chamber ioB or the pressure in the first plenum chamber ioA is less than the pressure set-point required to open the pressure relief v&ve 521.

As described in reference to the second embodiment of the invention, the passage 513A has a small diameter so that is has a large flow resistance, resulting in a low flow rate of the formulation flowing between the intermediate chamber 510B and the formulation chamber 509 during equalisation thereof. Therefore, when all of the formulation contained in the formulation chamber 509 has been expelled therefrom or the pressure in the formulation chamber 509 is less than the pressure set-point of the pressure relief valve 521 due to the release of formulation from the formulation chamber 509, the formulation contained in the intermediate chamber 5ioB will flow into the formulation chamber 509 gradually. Thus, it will take a certain period of time for the formulation in the intermediate chamber noB to flow into the formulation chamber 509 via the passage 513A to re-pressurise the formulation chamber 509 to a pressure greater than io the pressure set-point of the pressure relief valve 521 and so, after inhalation of the formulation, the user must wait said period of time before the actuation valve 517 may again be opened to release another dosage of formulation for inhalation. This means that the inhaler 501 has the advantage of releasing a metered dosage of formulation with a time delay between successive dosages to ensure that the user may not consume more than a pre-determined amount of formulation within a certain time period.

Although in the above described embodiment the equalisation member comprises a flexible bag 511 of impermeable material that contains the formulation chamber 509 and the intermediate chamber 5ioB, in an alternate embodiment (not shown), the equalisation member comprises a piston that is slidably received within the cartridge so8 and seals the first plenum chamber 5ioA from the intermediate chamber 5ioB. In one such embodiment, a partitioning wall is provided between the piston and the cartridge outlet so8A, so that it is disposed between the formulation chamber 509 and the intermediate chamber 5ioB, and comprises a passage with a high flow resistance to provide fluid communication between the formulation chamber 509 and the intermediate chamber 5ioB. In another embodiment, the equalisation member comprises a portion of flexible impermeable material that forms dividing wall between the intermediate chamber 51DB and the first plenum chamber 5ioA. In such an embodiment, the dividing wall deforms to adjust the size of the first plenum chamber 5loA relative to the intermediate chamber noB to equalise the pressures therein. A partitioning wall is provided between the defonnable dividing wall and the cartridge outlet so8, so that it is disposed between the formulation chamber 509 and the intermediate chamber ioB, and comprises a passage with a high flow resistance to provide fluid communication between the formulation chamber 509 and the intermediate chamber 5ioB. -4°-

Although in the above described embodiment the flexible bag 511 contains the formulation chamber 509 and the intermediate chamber 510B, in an alternate embodiment (not shown) the formulation chamber 509 is not contained in the bag ii.

In such an embodiment, the flexible bag u contains the intermediate chamber ioB and is provided on the side of the wall 512 that is remote of the chamber outlet o8A.

The intermediate chamber ioB contains fonnulation for inhalation and is sealed from the first plenum chamber ioA by the bag 511. The formulation chamber 509 is provided in the cartridge o8 on the side of the wall 512 that is proximate to the chamber outlet 5oSA and is fluidly communicated with the intermediate chamber 51DB io by the passage 513A in the wall 512. The pressurised gas in the first plenum chamber ioA exerts a force on the bag n to compress the formubtion contained therein so that it is at the same pressure as the pressurised gas. Therefore, formulation will flow from the intermediate chamber 5ioB, via the passage 513A, to the formulation chamber 509 until the pressure in the intermediate chamber sioB and the formulation chamber 509 are equalised to a pressure above the pressure set-point.

In the above described embodiments the time delay that the user must wait between the release of successive dosages from the inhaler is j seconds. In other embodiments the time delay may be, for example, between 0.5 seconds and thirty minutes. The time delay may be predetermined by selecting, for example, the diameter or length of the passage between the first and second plenum chambers, the pressure of the fluid in the first and second plenum chambers, or the pressure set-point of the pressure relief valve, which may be adjusted by adjusting the force of the biasing means. It should be recognised that inhalers having other lengths of time delay outside the above range are also intended to fall within the scope of the invention.

In the above described embodiments the formulation passage 6A, io6A, 206A, 406A, o6A may comprise a spray nozzle (not shown) that is configured so that formulation is expefled from the mouthpiece as a spray. In one such embodiment, the spray nozzle comprises restriction having a reduced cross-sectional area to increase the vdocity of formulation travelling through the formifiation passage 6A, io6A, 2o6A, 4o6A, o6Aso that the formulation is atomised.

Although in the above described embodiments the inhaler comprises a pressure relief valve, in alternate embodiments (not shown) the pressure relief valve may be omitted.

In one such embodiment, the pressure relief valve is replaced by an actuation valve.

The actuation valve may be similar to those previously described, comprising a diaphragm that is configured to open the actuation valve when the user inhales or a button that is configured to open the actuation valve when the user presses the button.

The actuation va've is configured so that when it is opened it fiuiffly communicates the cartridge outlet with the formulation outlet. Therefore, when the user opens the actuation valve, formulation contained in the formulation chamber will be expelled from the formulation chamber as the pressure therein is higher than the atmospheric pressure at the exit of the formulation outlet. Formulation will continue to be expelled from the formulation chamber until the pressure therein is equal to the outlet pressure, io at which point there will be no pressure difference between the pressure in the formulation chamber and the pressure at the exit of the formulation outlet and so no further formulation will be released or formulation will be released at a low flow rate as fluid gradually flows between the intermediate chamber and the formulation or first plenum chamber to restore the pressure in the formulation chamber. Therefore, the user is prevented from taking successive large dosages of formulation in a short period of time, and must instead close the actuation va've and wait for the formulation chamber to repressurise.

In order to address various issues and advance the art, the entirety of this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced and provide for a superior inhaler. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and teach the claimed features. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope and/or spirit of the disclosure. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. In addition, the disdosure indudes other inventions not presently claimed, but which may be claimed in future.

Claims

Claims 1. An inhaler comprising a first plenum chamber for containing a pressurised fluid, a formu ation chamber for containing a formulation fluid for inhalation and having a chamber outlet with a valve therein for the release of formulation fluid therefrom for inhalation by a user when the valve is open, an intermediate chamber, an equalisation member that seals the intermediate chamber from one of the formulation chamber and the first plenum chamber and is configured to equalise the pressure in the intermediate chamber and the one of the formulation chamber and the first plenum io chamber, and a passage to provide fluid communication between the intermediate chamber and the other one of the formubtion chamber and the first plenum chamber so that fluid will flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber to restore the pressure in the formulation chamber to a pressure above a pressure set-point in response to a pressure drop in the formulation chamber to below the pressure set-point due to a release of formulation fluid from the formulation chamber.
2. An inhaler according to claim 1, wherein the flow resistance of the passage is selected such that the rate of flow of fluid between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is restricted so that, following a pressure drop in the formulation chamber, the pressure in the formulation chamber is gradually restored to a pressure above the pressure set-point.
3. An inhaler according to claim 2, wherein the flow resistance of the passage is selected such that the rate at which the pressure in the formulation chamber is gradually restored is slower than the rate at which the pressure in the formulation chamber drops when formulation fluid is released from the formulation chamber, so that it takes a predetermined period of time for the pressure in the formulation chamber to bc restored to a prcssure above the pressure set-point.
4. An inhaler according to any of daims ito 3, wherein the combined v&ume of the intermediate chamber and the one of the formuthtion chamber and first plenum chamber is constant, and the equalisation member forms a boundaiy therebetween that adjusts to alter the relative volumes of the intermediate chamber and the one of the formulation chamber and first plenum chamber to equalise the pressures therein. -43 -
5. An inhaler according to any of claims 1 to 4, wherein the intermediate chamber comprises a second plenum chamber that is suitable for containing a pressurised fluid and the equalisation member seats the formulation chamber from the second plenum chamber and is configured to equalise the pressure in the formulation and second plenum chambers, and wherein the passage provides fluid communication between the second plenum chamber and the first plenum chamber so that pressurised fluid in the first plenum chamber flows into the second plenum chamber to restore the pressure in the second plenum chamber and in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber and in the io second plenum chamber to below said pressure set-point due to a release of formulation fluid from the formulation chamber.
6. An inhaler according to ciaim 5, wherein the equalisation member comprises a flexible diaphragm of impermeable material that separates the formulation chamber from the second plenum chamber and deforms to equalise the pressure in the formulation and second plenum chambers.
7. An inhaler according to claim 6, wherein the flexible diaphragm comprises a bag, the formulation chamber being defined by the interior of the bag and the second plenum chamber being defined by the exterior of the bag such that pressurised fluid in the second plenum chamber exerts a force on the formulation fluid in the formulation chamber through the bag.
8. An inhaler according to claim 6, wherein the flexible diaphragm comprises a bag, the formulation chamber being defined by the exterior of the bag and the second plenum chamber being defined by the interior of the bag such that pressurised fluid in the second plenum chamber exerts a force on the formulation fluid in the formulation chamber through the bag.
9. An inha'er according to daim 8, wherein the first plenum chamber is a'so defined by the interior of the bag and the bag further comprises a constriction that is disposed between the first and second plenum chambers and comprises the passage that provides fluidly communication between the first and second plenum chambers.
10. An inhaler according to claim 5, wherein the equalisation member comprises a piston that separates the formulation chamber and the second plenum chamber, said piston being sBdeabe to adjust the relative volumes of the formdation and second p'enum chambers to equaBse the pressures therein.
11. An inhaler according to any of claims 1 to 4, wherein the intermediate chamber is suitable for containing a formulation fluid for inhalation and the equalisation member seals the intermediate chamber from the first plenum chamber and is configured to equalise the pressure in the intermediate and first plenum chambers, and io wherein the passage provides fluid communication between the formulation chamber and the intermediate chamber so that formulation fluid in the intermediate chamber flows into the formulation chamber to restore the pressure in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber to below said pressure set-point due to a release of formulation thud from the form tilation chamber.
12. An inhaler according to daim ii, wherein the equaBsation member comprises a flexible diaphragm of impermeable material that separates the intermediate chamber from the first plenum chamber and deforms to equalise the pressure in the intermediate and first plenum chambers.
13. An inhaler according to claim 12, wherein the flexible diaphragm comprises a bag, the formulation chamber and the intermediate chamber being defined by the interior of the bag and the first plenum chamber being defined by a portion of the exterior of the bag such that pressurised fluid in the first plenum chamber exerts a force on the formulation fluid in the intermediate chamber through said portion of the bag.
14. An inhaler according to claim 13, wherein the bag further comprises a constriction that is disposcd bctwccn the formulation chamber and the intermediate chamber and comprises the passage that provides fluidly communication between the formulation and intermediate chambers.i. An inhaler according to daim 13 or daim 14, wherein the first plenum chamber is sealed from the portion of the bag that forms the formulation chamber. -45 -16. An inhaler according to any preceding claim, comprising an actuating mechanism including an actuator and an actuation valve, the actuation valve being moveable from a closed position to an open position in response to actuation of the actuator by the user to unblock the chamber outlet.17. An inhaler according to claim 16, having a biasing means that is configured to bias the actuation valve into the closed position.18. An inhaler according to claim i6 or claim 17, wherein the actuator comprises a io diaphragm that deforms to move the actuation va've into the open position in response to inhathtion by the user.19. An inhaler according to claim iS, wherein the diaphragm partitions the inside of the housing into first and second compartments and one of the first and second compartments comprises a suction channd so that the diaphragm deforms in response to the application of suction to the suction channel.20. An inhaler according to claim 16 or claim 17, wherein the actuator comprises a button that is depressible by the user to move the actuation valve into said open position.21. An inhaler according to claim 20, comprising a lever, and wherein the actuation valve comprises a valve head and a valve seat and is configured so that when the actuation valve is in the closed position the valve stem receives the valve head to block the chamber outlet, and wherein the lever engages with the valve head and the actuator is depressible inwardly towards the longitudinal axis of the outer housing to cooperate with the lever to urge the valve head away from the valve stem to move the actuation valve to the open position to unblock the chamber outlet.22. An inha'er according to any of daims i6 to 21, wherein the valve comprises the actuating valve.23. An inhaler according to any of daims ito 21, wherein the valve comprises a pressure relief valve that is configured to open when the pressure in the formulation chamber is above said pressure set-point.24. An inhaler according to claim 23, wherein the pressure relief valve comprises a valve housing and a valve head that is slidable within the valve housing between first, second and third positions, wherein in the first and second positions the valve head is configured to bthck the chamber outlet and in the third position the vahe head is configured to unblock the chamber outlet, the valve head being moveable from the first position to the second position upon inhalation by the user and moveable from the second position to the third position tinder the influence of the pressure of the formulation fluid in the formulation chamber, when said pressure is above said pressure set-point. I025. An inhaler according to daim 24, comprising a suction channel disposed on an opposite side of the valve head to the chamber outlet and configured so that when a user inhales through the suction channel a force is exerted on the valve head that urges the valve head away from its first position.26. An inhaler according to daim 24 or 25, wherein when the valve head is in the first position a reduced surface area of the valve head is fluidly communicated with the chamber outlet, and wherein when the valve head is in the second and third positions an increased surface area of the valve head is fluidly communicated with the chamber outlet.27. An inhaler according to claim 26, wherein the pressure relief valve comprises a valve seat that surrounds the periphery of the chamber outlet and the valve head is urged against the valve seat in said first position so that a reduced surface area of the valve head is fluidly communicated with the chamber outlet, an increased surface area of the valve head being fluidly communicated with the chamber outlet when the valve head is in the second and third positions.28. An inhalcr according to claim 26 or claim 27, whcrcin the valve head comprises a first section of reduced cross-section that comprises a first face and a second section of increased cross-section that comprises a second face, and wherein when the valve head is in the first position the first face is fluidly communicated wIth the chamber ouflet and the second face is sealed therefrom and when the valve head is in the second and third positions the first and second faces are both fluidly communicated with the chamber outlet.29. An inhaler according to claim 28, wherein the valve housing comprises a first section of reduced cross-section that is proximate to the chamber outlet and a second section of increased cross-section that is remote to the chamber outlet, and wherein when the valve head is in the first position the first section of the v&ve head is received in the first section of the valve housing to seal against the inside surface thereof to seal the second face from the chamber outlet, and wherein when the valve head in the second and third positions the first section of the valve head is received in the second section of the valve housing to provide fluid communication between the second surface and the chamber outlet. I030. An inhaler according to any of daims 24 to 29, wherein the valve housing comprises a peripheral wall and an outlet channel to vent the formulation fluid from the inhaler for inhalation by the user, wherein when the valve head is in the first and second positions the valve head seals against the peripheral wall of the valve housing to seal the chamber outlet from the outlet channel, and wherein when the valve head is in the third position the outlet channel is fluidly communicated with the chamber outlet.31. An inhaler according to any of claims 24 to 30, wherein the pressure relief valve comprises a biasing means to bias the pressure relief valve into the first position.32. An inhaler according to any preceding claim, comprising a cartridge having a partitioning wall, wherein the formulation chamber, intermediate chamber and first plenum chamber are formed in the cartridge and the partitioning wall separates the intermediate chamber from the other one of the formulation chamber and the first plenum chamber, wherein the passage that fluidly communicates the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is formed in said partitioning wall.33. An inhalcr according to claim 32, wherein thc cartridge is rcmovaby received in o the housing.34. An cartridge for an inhaler comprising a first plenum chamber for containing a pressurised fluid, a formulation chamber for containing a formulation fluid for inhalation and having a chamber ouflet for the r&ease of formulation fluid therefrom for inhalation by a user when a v&ve is open, an intermediate chamber, an equalisation member that seals the intermediate chamber from one of the formulation chamber and the first plenum chamber and is configured to equalise the pressure in the intermediate chamber and the one of the formulation chamber and the first plenum chamber, and a passage to provide fluid communication between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber so that fluid will io flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber to restore the pressure in the formulation chamber to a pressure above a pressure set-point in response to a pressure drop in the formulation chamber to below said pressure set-point due to a release of formulation fluid from the formulation chamber.35. A cartridge according to daim 34, wherein the flow resistance of the passage is sdected such that the rate of flow of fluid between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is restricted so that, following a pressure drop in the formulation chamber, the pressure in the formulation chamber is gradually restored to a pressure above said pressure set-point.36. A cartridge according to claim 35, wherein the flow resistance of the passage is selected such that the rate at which the pressure in the formulation chamber is gradually restored is slower than the rate at which the pressure in the formulation chamber drops when formulation fluid is released from the formulation chamber, so that it takes a predetermined period of time for the pressure in the formulation chamber to be restored to a pressure above said pressure set-point.3. A cartridge according to any of daims 34 to 36, whcrein the combined volume of the intermediate chamber and the one of the formulation chamber and first plenum chamber is constant, and the equalisation member forms a boundary therebetween that adjusts to alter the relative volumes of the intermediate chamber and the one of the formulation chamber and first plenum chamber to equafise the pressures therein.38. A cartridge according to any of claims 34 to 37, wherein the intermediate chamber is suitable for containing a pressurised fluid and the equalisation member seals the formifiation chamber from the intermediate chamber and is configured to equalise the pressure in the formulation and intermediate chambers, and wherein the passage provides fluid communication between the intermediate chamber and the first plenum chamber so that pressurised fluid in the first plenum chamber flows into the intermediate chamber to restore the pressure in the intermediate chamber and in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber and in the intermediate chamber to below io said pressure set-point due to a release of formulation fluid from the formulation chamber.39. A cartridge according to claim 38, wherein the equalisation member comprises a flexible diaphragm of impermeable material that separates the formulation chamber from the intermediate chamber and deforms to equalise the pressure in the formulation and intermediate chambers.40. A cartridge according to claim 39, wherein the flexible diaphragm comprises a bag, the formulation chamber being defined by the interior of the bag and the intermediate chamber being defined by the exterior of the bag such that pressurised fluid in the intermediate chamber exerts a force on the formulation fluid in the formulation chamber through the bag.41. A cartridge according to claim 39, wherein the flexible diaphragm comprises a bag, the formulation chamber being defined by the exterior of the bag and the intermediate chamber being defined by the interior of the bag such that pressurised fluid in the intermediate chamber exerts a force on the formulation fluid in the formulation chamber through the bag.42. A cartridge according to daim 41, wherein the first penuim chamber is also defined by the interior of the bag and the bag further comprises a constriction that is disposed between the intermediate chamber and the first p'enum chamber and comprises the passage that provides fluidly communication between the intermediate and first plenum chambers.43. A cartridge according to claim 38, wherein the equalisation member comprises a piston that separates the formulation chamber and the intermediate chamber, said piston being slideabe to adjust the relative volumes of the formdation and intermediate chambers to equalise the pressures therein.44. An cartridge according to any of claims 34 to 37, wherein the intermediate chamber is suitable for containing a formulation fluid for inhalation and the equalisation member seals the intermediate chamber from the first plenum chamber and is configured to equalise the pressure in the intermediate and first plenum io chambers, and wherein the passage provides fluid communication between the formulation chamber and the intermediate chamber so that formulation fluid in the intermediate chamber flows into the formulation chamber to restore the pressure in the formulation chamber to a pressure above said pressure set-point in response to a pressure drop in the formulation chamber to below said pressure set-point due to a release of formtilation fluid from the formuthtion chamber.4. An cartridge according to claim 44, wherein the equafisation member comprises a flexible diaphragm of impermeable material that separates the intermediate chamber from the first plenum chamber and deforms to equalise the pressure in the intermediate and first plenum chambers.46. A cartridge according to claim 45, wherein the flexible diaphragm comprises a bag, the formulation chamber and the intermediate chamber being defined by the interior of the bag and the first plenum chamber being defined by a portion of the exterior of the bag such that pressurised fluid in the first plenum chamber exerts a force on the formulation fluid in the intermediate chamber through said portion of the bag.47. A cartridge according to claim 46, wherein the bag further comprises a constriction that is disposed between the formulation chamber and the intermediate chamber and comprises the passage that provides fluidly communication between the formulation and intermediate chambers.48. A cartridge according to daim 46 or claim 47, wherein the first p'enum chamber is sealed from the section of the bag that forms the formulation chamber.49. A cartridge according to any of claims 34 to 48, comprising a partitioning wall that separates the intermediate chamber from the other one of the formulation chamber and the first p'enum chamber, wherein the passage that fluid'y communicates the intermediate chamber and the other one of the formulation chamber and the first plenum chamber is formed in said partitioning wall.50. A nicotine delivery system comprising the inhaler according to any of claims ito 33.w 51. A method of controlling the delivery of formulation thud from an inhaler comprising the steps of: providing formulation fluid for inhalation in a formulation chamber at a pressure above a pressure set-point required to release formulation fluid therefrom for inhalation by a user; providing pressurised fluid in a first plenum chamber at a pressure above the pressure set-point, the pressure in one of the first plenum chamber and the formulation chamber being equalised with the pressure in an intermediate chamber by an equalisation member; releasing formulation fluid from the formulation chamber in response to inhalation by a user so that the pressure therein drops to below the pressure set-point; and, allowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber to restore the pressure in the formulation chamber to a pressure above the pressure set-point.52. A method according to claim 51, wherein the step of allowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber to restore the pressure in the formulation chamber comprises allowing fluid to flow between thc intermediate chamber and the other one of the formulation chamber and the first plenum chamber at a restricted rate of flow so that the pressure in the formuflation chamber is gradually restored to a pressure above the pressure set-point.53. A method according to claim 52, wherein the step of allowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first pknum chamber at a restricted rate of flow comprises allowing fluid to flow between the intermediate chamber and the other one of the formulation chamber and the first plenum chamber at a flow rate at which the rate at which the pressure in the formulation chamber is gradually restored is slower than the rate at which the pressure in the formulation chamber drops when formulation fluid is released from the formulation chamber, so that it takes a predetermined period of time for the pressure in the formulation chamber to be restored to a pressure above the pressure set-point.