HK1117477B - A pressure control device, a container comprising the pressure control device and a method for preparing a beverage container and the pressure control device - Google Patents

Description

Pressure control device, container comprising a pressure control device and method of manufacturing a beverage container, pressure control device

Technical Field

The present invention relates to a pressure control device for controlling the pressure in a storage compartment of a container.

Background

The product to be dispensed from the container in a pressurized state is pressurized in the container by means of, for example, a pressure medium, such as a pressure gas. Thus, in the same compartment containing the product to be dispensed, the pressure medium is provided in the container at a higher overpressure. Such a pressure medium, in particular a pressure gas, will for example collect in the head space above the product being dispensed. Initially in the use of such containers, although high dispensing pressures may prevail, the pressure decreases as more and more product is dispensed from the container. The practical situation is as follows: a part of the pressure medium will leave the container together with the product and, in addition, the space occupied by this reduced amount of pressure medium will increase gradually.

In order to overcome this drawback, it has been proposed to provide a compartment in or on the container, in which compartment a quantity of pressure medium is stored, which pressure medium can be dispensed from the container in a dose by means of a pressure control device. Such a device is known, for example, from WO 99/47451.

In this known device a pressure control device is provided, which device comprises a pressure control chamber with at least one movable wall part. The pressure control chamber is closed with respect to the surroundings and provides a certain control pressure in the pressure control chamber, for example in a chamber filled with a control gas or air. The movable wall part operates the valve means so that if in the space with the beverage the pressure changes in relation to the control pressure in the pressure control chamber, in particular if the pressure decreases as a result of the beverage being dispensed, the movable wall part will change position and the valve means will temporarily open, as a result of which pressurized gas flows from the compartment into the space where the beverage is held. If the pressure in this space once again reaches a desired value approximately equal to the control pressure, the movable wall part is pressed back to the initial position and the valve mechanism is closed.

With this known mechanism, the following drawbacks arise, namely: gas can flow from the surroundings into the pressure control chamber and vice versa, so that the gas composition and its volume in the pressure control chamber can vary undesirably. As a result, different equilibrium states may result. The fact is that an increase of the amount of gas in the pressure control chamber and/or a change of its compressibility will affect a change of the control pressure, so that a different equilibrium will be obtained for the pressure in the space with the beverage. This is disadvantageous both with respect to the quality of the beverage and its dispensability, in particular with respect to gas-containing beverages, such as carbonated beverages.

In this respect, the same or similar disadvantages occur both when the device is used for other liquids, pasty substances or gases, for example, and when a liquid is used in the pressure control chamber.

Disclosure of Invention

It is an object of the present invention to provide a pressure control device for a container containing a medium, by means of which at least some of the drawbacks of the known devices can be eliminated while maintaining the advantages of the known devices.

It is an object of the invention, inter alia, to provide a beverage control device by means of which the same control pressure can be maintained for a long time.

It is a further object of this invention to provide such a pressure control device which can be stored for a period of time at atmospheric conditions and which, when subsequently used, each time has a preselected control pressure in the pressure control chamber for a predetermined use.

At least some of these and other objects are achieved by the pressure control device of the present invention.

The invention provides a pressure control device for a container containing a medium which is liquid or gaseous, comprising a pressure control chamber and a gas reservoir, the pressure control chamber having at least one movable wall part for operating a mechanism for opening and/or closing a gas supply port of the gas reservoir for allowing pressure gas to flow from the gas reservoir to the pressure control chamber, wherein a scavenger is contained in the pressure control chamber.

With the pressure control device of the present invention, a scavenger is included in the pressure control chamber to trap gas that flows into the pressure control chamber during use. As a result, during use, no change in gas composition and/or gas volume is induced by the gas flowing into the pressure control chamber in order to maintain the control pressure.

As scavenger it is preferably suitable to incorporate a gas which is used as a pressure gas in the beverage dispensing device. For carbonated beverages, for example, scavengers suitable for capturing carbon dioxide are generally adapted.

Any suitable type of scavenger, such as chemically bound, adsorbed and/or absorbed scavengers, may be employed with the pressure control device of the present invention. Preferably, the scavenger is contained in the pressure control chamber and is made independent of the medium being dispensed in the particular beverage. Therefore, impurities can be removed. The scavenger may be inserted into the pressure control chamber as an unsecured item or confined within its housing. The scavenger may form an integral part of the device, e.g. fixedly attached to the wall.

The scavenger used in the pressure control device of the present invention is preferably derived from CO₂A group of adsorbents and/or absorbents, for example carbon, in particular activated carbon, diatomaceous earth, clay, aluminium silicate, zeolite or silicate. In principle, liquids and solutions, in particular alkaline materials, can also be used.

The present invention also provides a container comprising the above pressure control device and a liquid and/or gas, wherein: the pressure control means is at least partly contained in the liquid and/or gas.

Such containers are particularly suitable for storing and dispensing media such as beverages at controlled pressures.

In a particularly desirable embodiment, the container of the invention is designed to be able to dispense carbonated beverages, while carbon dioxide is used as the pressure gas, in particular carbon dioxide having a purity acceptable by FDA standards, which is introduced directly into the beverage during use, while the pressure control chamber of the pressure control device contains CO₂A scavenger.

The present invention also provides a method for manufacturing a beverage container, comprising the steps of: manufacturing the pressure control device; making a beverage container; introducing a beverage and a pressure control device into the beverage container; closing the beverage container; wherein: the pressure control means is stored at atmospheric pressure prior to contacting the beverage with the pressure control means.

The advantages of this method are: the beverage container and the pressure control device can be manufactured, transported and stored separately without pressure changes, while the pressure can be controlled at a desired range all the time during use. Preferably, the pressure is then controlled so as to create an equilibrium between the medium being dispensed and the head space in the container.

The present invention also provides a method for manufacturing a pressure control device, wherein: a pressure control chamber having at least one movable wall portion is manufactured, the chamber being associated with a valve assembly operable by said wall portion, while a scavenger is provided in the pressure control chamber.

Drawings

For the purpose of illustrating the invention, there will now be described illustrative embodiments thereof with reference to the accompanying drawings.

FIG. 1 schematically shows the apparatus of the invention in a cutaway side view;

figure 2 shows schematically, in a sectional view, a pressure control member for use in the device of the invention.

Figure 3 schematically shows an alternative embodiment of the pressure control device of the invention.

Fig. 4 schematically shows a second alternative embodiment of the pressure control device of the invention.

Detailed Description

In the description, identical or corresponding parts have corresponding reference numerals. In this description, embodiments are described with reference to a tapping device for carbonated beverages, in particular beer. However, it should be understood that: other uses also exist, such as the use of the device for dispensing food products, foam products, paste-like objects and the like.

Fig. 1 shows a device 1 according to the invention provided with a container 2 in which a quantity of beer 3 to be dispensed is contained in a first compartment 4. In the embodiment shown, the container 2 is a thin-walled tank with a large volume (e.g. 3 or 5 liters). The container 2 is completely closed all around and its top surface is provided with a central hole 6 for receiving a dispensing means 7 which will be further described below. A pressure control device 8, which will be described further below, extends below the distribution device 7. A transfer device 9 for discharging the beer 3 from the container 2 to a glass (not shown) via the dispensing device 7 is connected to the dispensing device 7. To this end, a dip tube 10 extends from the dispensing device 7 to a position adjacent to the bottom 11 of the container 2, so that the entire beer 3 can be dispensed through the dispensing device 7 and the transferring device 9.

The dispensing means 7 comprise a passage 12 which is connected to the dip tube 10 inside the container 2 and to the transfer means 9 outside the container 2. The dispensing device 7 further comprises a seal (not shown) which can be opened against the spring pressure and which, in a first position, seals the device 7 and, in a second position, places the immersion tube 10 in fluid communication with the transfer device 9 and into which the at least one conduit 13 projects. For operating the dispensing device 7, a push button 14 is provided which, upon movement in the direction of the top surface 5, is able to move the sealing means into the second position by means of said spring pressure, and, when not actuated, is able to move it in the direction of the first position in order to seal the device. Such dispensing devices 7 are known per se and, within the framework of the invention, can be applied or replaced by the skilled person in a known suitable manner.

The pressure control device 8 comprises a cassette 15 comprising a second compartment 16. Adjacent to the top end of the box 15 is arranged a pressure control member 17 which will be further explained. The cassette 15 is suspended from the top surface 5 or the dispensing unit 7 by means of suspension means 18 so that the channel 19 of the pressure control member 17 is located at a distance below the dispensing unit 7, preferably above the liquid level. The pressure control means 8 and the dispensing means 7 are preferably interconnected in such a way that they can be inserted into the top surface 5 through the central hole 6, and that the hole 6 is closed by the dispensing means 7 in order to provide gas-and liquid-tightness. Thus, the pressure control device 8 is easy to arrange, while at the same time it can be easily removed, at least at the working position provided for this purpose, for repeated use or recycling.

A filler 20 adapted to bind a quantity of generant is preferably disposed in the second compartment 16. In the second embodiment shown, the filling 20 is designed as a mass of activated carbon fibers having a large specific internal and external surface area for absorbing a large amount of CO thereon or therein at an acceptable gas pressure within the second compartment 16₂。

In a preferred embodiment, 600-1400 m can be preferred²Activated carbon (in particular activated carbon fibers with a large specific surface area) with/gr and a high internal porosity (in particular more than 55% and preferably 55-80%) is used as filler. In addition, the fibers preferably have a relatively large outer specific surface, e.g. greater than 2dm³Especially greater than 25dm³. Such activated carbon fibers are commercially available. The advantages of using such fibers are: the second compartment may be of a smaller construction while still being able to incorporate sufficient CO₂. It can be seen by way of illustration that a container with a volume of 5 litres of beer is completely emptied at 7 ℃ and an ideal internal pressure of 1.7 barA second compartment having a capacity of about 40ml is sufficient with a gas pressure in the second compartment of about 10 bar. In the embodiment shown, a slightly larger second compartment and the same pressure (and thus a larger amount of propellant) have been selected to obtain a safety factor in order to prevent complete emptying of the container. For example, the ratio of the capacity of the first compartment to the capacity of the second compartment may be selected to be > 140: 1, such as 66: 1. In view of the desired outside dimensions of the relative capacity of the device, it is preferred that the ratio is greater than 5: 1, more preferably greater than 15: 1, and most preferably greater than 50: 1. For complete emptying of the above-mentioned container with a volume of 51, measured at a pressure of 1 bar, it is suitable to use approximately 18 litres of CO₂A gas. It should be immediately understood that: in order to obtain an arbitrary volume of the first compartment and a desired overpressure therein, the CO should be predetermined in addition to the desired volume of the second compartment in relation to pressure and temperature₂And the desired volume of the filler. If the filling is omitted, a compartment capable of storing gas under pressure at a higher pressure or a larger compartment should be used. In addition, it should be clear that: other fillers may be used, depending on the application chosen, in particular the booster used. For example, acidified clays, activated aluminum and alumina, iron oxide, magnesium oxide, silica gel, liquids such as acetone, and the like may be used. Use of CO in beverages, in particular carbonated beverages and other products suitable for consumption₂It is possible to provide an advantage that it does not cause any adverse effect on the user in normal use. In addition, CO can be obtained relatively easily₂Such as waste from industrial production, which is reused to be environmentally friendly.

The pressure control device 8 is for example provided with pressure control means 17, which are shown in more detail in fig. 2 and which are themselves disclosed for example in particular by US-5,368,207, it being understood that the publication relating to these pressure control means can be referred to in the present application. These Pressure control means, also known as Pressure generators, are provided in particular by the Stabilpress company of Belgium. The pressure control member 17 comprises a cylindrical housing 20 closed at a first end by a bottom 21 and provided at its opposite end with a passage 19. During use, the channel 19 is directed towards the first compartment 4 and is in fluid communication therewith. Inside the housing 20 a somewhat hourglass-shaped piston body 22 is accommodated, which is provided at either end with an O-ring or similar sealing 23 against the inside of the housing 20. Between the first end 24 of the piston body 22 and the bottom 21 a piston chamber 25 is formed, the size of which varies in accordance with the axial displacement of the piston body 22 in the housing 20. At the location of the waist 26 of the piston body 22, a plurality of holes 27 are provided in the housing 20, which holes are in fluid communication with the second compartment 16. On the inside of the housing 20, a circular groove 28 is provided between the hole 27 and the channel 19, so that a somewhat limited fluid connection is formed between the second compartment 16 to the first compartment 4 via the hole 27, the space between the O-ring 23 and the groove 28 and the channel 19, when the O-ring mounted adjacent the second end 29 extends at the level of the groove 28. Subsequently, gas having a higher pressure can flow from the second compartment 16, through the fluid communication, into the first compartment 4, whereby the pressure in the first compartment 4 increases. A reference pressure is provided in the piston chamber 25 which corresponds substantially to the desired pressure in the first compartment 4. If necessary, a spring means or the like may be provided in the first chamber to achieve said reference pressure. If the desired pressure in the piston compartment has been reached, the piston body 22 is moved axially in the direction of the bottom 21 in order to achieve the reference pressure in the piston chamber 25, in which state the O-ring 23 adjacent to the second end 29 seals the above-mentioned fluid passage, since the O-ring 23 then abuts against the inside of the housing 20 between the hole 27 and the groove 28. If a portion of the beer is discharged from the first compartment 4 by means of the dispensing device 7, the pressure therein will drop and as a result the piston body 22 will be moved axially in the direction of the passage 19 under the influence of the pressure in the piston chamber 25, so that gas can flow again from the second compartment 16 into the first compartment 4 along the above-mentioned fluid connection under the influence of the high pressure in order to restore the desired pressure therein. When this is reached, the piston body 22 is pushed again into the closed position. In this way, by means of the pressure control, a constant desired pressure can always be maintained in the first compartment. Improvements to these pressure elements are disclosed in particular in the abovementioned U.S. Pat. Nos. US5,368,207, WO00/35777 and FR 2690142.

Due to the pressure control member 17 of the present invention, the housing 20 and/or the piston body 22 are preferably made of plastic. This is relatively light and easy to handle. During use, a pressure gas (in particular CO) is present₂) For example, through the housing 20, through the piston body 22 and/or along the seal 23 into the piston chamber 25. As a result, the amount of gas in the piston chamber 25 will undesirably increase, so that pressure changes will occur, as a result of which different equilibrium conditions will be set. The practical situation is as follows: will move the piston body 22 away from the bottom 22 so that more pressure will be required at the opposite 2 nd end 29 in order to return the piston to the same condition as the secondary pressure gas flows into the piston chamber 25. In addition, there is a risk that: the compressibility of the gas mixture in the piston chamber 25 will vary as a result thereof. In order to avoid these drawbacks, it is proposed according to the invention to provide in the piston chamber 25 a scavenger 31 for trapping said pressure gas flowing into the piston chamber 25. Of course, the scavenger is selected so that it ensures the trapping of the gas under pressure, and not the gas, in particular air or its components (in particular oxygen), initially introduced into the piston chamber 25. The scavenger 31 does not undergo any volume change in relation to the pressure in the piston chamber 25 when trapping the pressure gas.

If it is to be mixed with CO₂Used as a pressure gas, preferably from CO₂An adsorption and/or absorption agent (for example carbon), in particular activated carbon, diatomaceous earth, clay, aluminium silicate, zeolite or silicate. In principle, liquids and solutions, in particular alkaline materials, can also be used.

For other pressurized gases such as nitrogen, suitable scavengers will immediately occur to those skilled in the art.

Preferably, overpressure relief means (not shown) are provided in the first and second compartments, at the ends of which known valves or the like are typically employed.

As shown in fig. 1, a filter device 30 is provided in the second compartment 16 to filter particles of the filling 20 (in particular relatively small activated carbon particles which may adversely affect the quality of the product being dispensed and the health of the user) from the airflow. In addition, clogging and damage can therefore also occur. The filter device 30 may be designed in various ways (e.g., mesh, foam, fabric, semi-permeable polymer, and the like). By having the filter means 30 located in the second compartment 16, contact between the dispensed fluid 3 and the filter means 30 can be avoided. In addition, particles of the filler 20 can be prevented from ending up in the pressure control member 17. In practice, the filter means 30 may also be arranged in the passage hole 27. The filter means 30 may be arranged in the second compartment 16, for example before being closed by the pressure control member 17.

The apparatus of fig. 1 may be used in the following manner.

Through the hole 6, a suitable amount of beer 3 is introduced into the first compartment 4. Subsequently, the container 2 with the beer can be treated, for example pasteurized, for which purpose a temporary seal can be provided in the bore 6. Thereafter, the pressure control device 8 together with the dip tube 10 and the dispensing device 7 is inserted into the container 2 through the aperture 6, and the dispensing device 7 is secured in order to close the aperture 6, for example by means of a seal. During insertion of the pressure control device 8, the piston body 22 can be brought out of the closed position in which the second end 29 seals against the channel 19 in order to pressurize the first compartment 4. The filling is preferably effected with an overpressure so that the pressure in the first compartment 4 is at least equal to and preferably greater than the desired operating pressure in the head space of said first compartment 4. In a preferred embodiment described previously, this means that the filling takes place, for example, at a minimum pressure of 1.65 bar (preferably slightly higher). This ensures that the control device is kept in the closed position during filling, so that CO can be avoided₂Prematurely escaping from the second compartment. Thus, the second compartment is filled and assembled already before the first compartment 1 is filled. In addition, in each case, the desired pressure can be automatically achieved and maintained. If the consumer wants to take the beer out of the first compartment, the transfer device 9 can be positioned on the dispensing device 7, after which it is positionedThe channel 12 is opened by simply pressing the button 14 and the beer 3 is dispensed in the desired amount through the dip tube 10 and the conduit 13. Once the button 14 is released, the channel 12 is closed again as previously described. When the first compartment 4 has been completely emptied, the pressure control device 8 is optionally removed again for reuse or for separate recycling. The setting of the pressure control means may also be done by the user.

In an alternative solution, the dispensing device 7 with the transfer device 9, the dip tube 10 and the pressure control device 8 are designed as a separately mountable unit assembly. For example, the cell assembly may be provided as a non-fastening component and may be manufactured in a refillable design.

Fig. 3 schematically shows a part of an alternative embodiment of the pressure control means 8 and an alternative embodiment of the pressure control member 17. In this embodiment, the pressure control device 8, at least the second compartment 16, is designed essentially as a container for liquefied gas known per se. It comprises a metal wall 15 with an outlet hole 40 at the top side, in which a valve 32 is arranged by means of a snap ring 41. This valve 32 is known per se as a liquefied gas valve and comprises a housing 33 in which, by means of a spring 34, a valve body 36 is pressed against a valve seat 38 in order to seal off a dispensing passage 27, which passage is formed in the embodiment shown by a portion 27a extending in the valve body 36, a portion 27b extending in the piston body 22 and a third portion 27c extending in the immersion tube in the second compartment 16. When the valve body 36 is pressed from the valve seat 38, an open connection is formed between the second compartment 16 and the space 43 in the housing 20 between the second end 29 of the piston body 22 and the snap ring 41, against the pressure of the spring 34. In order to equalize the pressure, at least one channel 19 is provided between the space 43 and the first compartment 4.

In this embodiment, the piston body 22 is pressed against the valve body 36 by means of the seat 44, while an open connection is formed between the channel parts 27a and 27 b. On the side of the piston body 22 remote from the space 43, a piston chamber 25 with a scavenger 31 therein is formed between the bottom 21 and the first end 24 of the piston body 22. The housing 20 is fixed to the flange 46 of the snap ring 41 by means of the snap edge 45, so that a fixed connection is obtained.

An embodiment of the pressure control device 8 of fig. 3 is further disclosed in the international patent application WO/0035774. A number of alternative embodiments, in particular the pressure control member 17, are also described in this publication, which embodiments are referred to in the present application and according to the invention a scavenger 31 can be provided.

In fig. 4, the pressure control device 8 of fig. 3 is shown with two alternative embodiments of scavengers 31a, 31b therein. In fig. 3, the scavenger 31 is contained in the piston chamber 25, for example in the form of a relatively solid part, such as a compressed block formed of powder or granules, which is mounted in the piston chamber 25 before the piston body 22 is arranged. Although the scavenger 31 has been provided as an unsecured body in the piston chamber 25, it may also be secured to the wall by, for example, gluing, sealing, welding or any other suitable means. In fig. 4, two possible solutions are shown which can be used separately from each other. In fig. 4, on the left side, a scavenger 31a is shown in the form of a box 47, which scavenger 31a holds the actual scavenger 31a, for example in the form of a powder or granules 48. The cassette 47 may be made of any suitable material as long as it is permeable to the pressurized gas. In fig. 4, a second embodiment is shown, in which the scavenger 31b is in the form of a direct connection to the bottom 21. In fig. 4, the bottom 21 is shown as a separate insert which is fixed in the housing 20 by, for example, clamping, gluing, welding or different direct fixing methods known to the person skilled in the art. The scavenger 31 may be formed by pressing, injection molding, cutting or the like from a scavenger containing material, such as a mixture of plastic and one of the possible scavenger materials mentioned above. Alternatively, the scavenger 31b may be designed as part of the bottom wall 21, for example by a double design of the bottom wall, while the side of the bottom 21 facing the piston chamber 25 is formed by said scavenger 31 b.

It should be understood that: the scavenger 31, 31a, 31b may be arranged in other ways and/or at other locations in the piston chamber 25, for example on a part of the piston body 22 or as a part of the piston body 22.

The invention is not to be limited in any manner by the illustrative embodiments described in the specification and drawings. Many variations thereon are intended to fall within the framework of the invention.

For example, the dispensing means and/or the transfer means can be designed differently, for example as known liquefied gases for obtaining a foam. They can also be designed for single time operation only, so that the entire first compartment can be emptied at one time. The container 2 can be manufactured in different ways and from different materials, such as steel, aluminium or plastic. In the illustrative embodiment shown, although a higher design is used for the container, it will be clear that different sizes (e.g. flatter) may be used in order to store the container in a relatively simple manner in a refrigerator or the like. In addition, various auxiliary agents (e.g., a coolant) may be provided according to the use. In the illustrative embodiment shown, the propellant is introduced in the first compartment above the liquid level during normal use, which largely prevents the gas flow from being dispensed through the fluid. In particular, premature foaming can thereby be prevented. But it should be understood that: if desired, different positions of the pressure control device may be selected to direct the propellant directly into the fluid being dispensed. Thus, for example, a completely ideal frothing can be obtained for so-called new products, soft drinks (such as a mixture of milk and ice cream, etc.) and the like.

It should be understood that: these and many similar variations are intended to fall within the framework of the invention.

Claims (14)

1. A pressure control device for a container containing a medium which is a liquid or a gas, the pressure control device comprising a pressure control chamber and a gas reservoir, the pressure control chamber having at least one movable wall portion for operating a mechanism for opening and/or closing a gas supply port of the gas reservoir to allow a flow of gas under pressure from the gas reservoir to the pressure control chamber, wherein a scavenger is contained in the pressure control chamber.

2. Pressure control according to claim 1An apparatus, wherein: the scavenger is designed for capturing at least CO in the pressure control chamber₂A gas.

3. The pressure control device according to claim 2, wherein: the scavenger is CO₂A scavenger.

4. The pressure control device according to claim 1, wherein: the scavenger is composed of CO₂The absorbent is selected from the group.

5. The pressure control device according to claim 1, wherein: the scavenger is composed of CO₂A selection from the group of adsorbents.

6. The pressure control device according to claim 1, wherein: the scavenger is composed of CO₂The absorbent and the adsorbent are selected from the group.

7. The pressure control device according to claim 1, wherein: the pressure control chamber is formed in a piston-cylinder assembly, the piston forming said movable wall portion, fixedly connecting the scavenger to one of the fixed walls of the pressure control chamber.

8. The pressure control device according to claim 1, wherein: which is at least partly made of plastic.

9. A container comprising the pressure control device of claim 1 and a liquid and/or gas, wherein: the pressure control means is at least partly contained in the liquid and/or gas.

10. The container of claim 9, wherein: the liquid or gas in the container comprises at least CO₂。

11. The container of claim 9 or 10, wherein: the pressure control device comprises a gas container in which gas under pressure is contained at a first pressure, while in the pressure control chamber a second pressure lower than the first pressure is present, said means for opening and/or closing the gas supply port of the gas container being designed to enable the pressure of the gas under pressure to be discharged from the gas container to the container in a controlled manner to an extent approximately equal to or higher than the second pressure.

12. The container of claim 11, wherein: the pressure gas being or at least comprising CO₂And the liquid is a carbonated beverage.

13. A method for making a beverage container comprising the steps of:

-manufacturing a pressure control device according to any one of claims 1 to 8;

-making a beverage container;

-introducing the beverage and the pressure control means into the beverage container;

-closing the beverage container;

wherein: the pressure control means is stored at atmospheric pressure prior to contacting the beverage with the pressure control means.

14. A method for manufacturing a pressure control device, wherein: a pressure control chamber having at least one movable wall portion is manufactured, the chamber being associated with a valve assembly operable by said wall portion, while a scavenger is provided in the pressure control chamber.