GB2291172A - Gas release valve - Google Patents

Abstract

A cutter 51 with a generally cylindrical blade 52 operable to rupture the diaphragm 35 sealing the flow path of a gas release valve is disposed opposite a correspondingly shaped annular support ring 55 lying radially within the cutting edge 56 on the other side of the diaphragm. In operation, the cutting edge pushes the diaphragm against the support ring before it ruptures reducing the energy required to shear the diaphragm. Preferably the radial spacing between the cutter and the support is substantially equal to the width of the diaphragm. <IMAGE>

Description

Gas Release Valve The present invention relates to release valves, and in particular to gas release valves.

Gas release valves are used to fill inflatable structures with compressed gas from cylinders containing liquefiable (C02) or permanent (N2) gas or a combination of the two e.g. CO2 + 4% N2. For convenience hereafter, the term 'gas' can be considered to cover these combinations i.e.

liquid or gas or both, depending on temperature and pressure. Typical uses are inflatable liferafts, rigid inflatable boats, self righting bags, and buoyancy bag inflation. The valves are easily actuated, and allow a high gas throughput.

Existing gas release valves for use with liferafts excessively restrict gas fluid flow which results in unacceptably long inflation times at low temperatures. Furthermore, expansion of the fluid C02 may solidify gas within the valve and block it. Existing valves do not utilise the energy in the stored gas in their operation. Also, they do not prevent debris carried by the compressed gas entering the chambers of the structure.

GB-A-2 172 095 discloses a ripcord release valve. Pulling a ripcord on the valve rotates a cam member. This acts upon a sharpened tappet which cuts through a metal disc as the cam turns, thereby releasing the compressed gas.

However, the operation of the valve is not instantaneous, and the force with which the ripcord must be pulled is relatively high.

The present invention seeks to provide a release valve that operates effectively instantaneously and which uses stored energy to cut through a disc and release the gas into the structure.

The invention proposes a gas release valve comprising a valve body adapted to be connected to a source of compressed gas and further adapted to be connected to an inflatable body, a gas flow path through the valve body from the source of compressed gas to the inflatable body, diaphragm means sealing the flow path, cutter means that is operable to rupture the diaphragm means, valve release means, and means to actuate the cutter member, wherein the cutter means comprises a blade of generally cylindrical form with a cutting edge at one annular end, and a correspondingly annular shaped support ring against which in operation the cutting edge pushes the diaphragm means before it ruptures, the ring lying radially within the cutting edge.

Preferably, the annular end of the blade has an acute angle cross-section which has an inner surface of uniform radius and an outer surface which increases in radius progressively away from the annular end.

Further, said inner surface radius is somewhat larger than the outer surface radius of the support ring. The difference in radii may correspond approximately to the thickness of the diaphragm means.

In order that the invention and its various other features may be understood more easily, an embodiment thereof will now be described by way of example only, with reference to the drawings, wherein: Fig.l is a plan view of a known release valve; Fig.2 is a view in direction 2 in Fig.l; Fig.3 is a section on 3-3 in Fig.l; Fig.4 is a detail of portion X in Fig.3; Fig.5 is a view of portion X in Fig.3 illustrating the modified cutter arrangement in accordance with the present invention; Fig.6 is an enlarged view of portion Y in Fig.5; and Fig.7 shows a cut diaphragm after release of the valve.

Figures 1 to 4 show a gas release valve of the type produced and made available by the present applicant under the code GIS Issue 1.

The release valve comprises an operating head 10, a cylinder valve 30, and a pick up tube 70. The release valve is screwed into a cylinder 80 containing compressed gas and is actuated by a lanyard 85. The release valve is connected to a hose (not shown in Figs 3 & 4) which leads to an inlet valve and a liferaft or other inflatable member.

The operating head 10 comprises a housing containing a cavity. The outside of the operating head has a flange 11. An actuating member 12, 13 is axially movable through the head. The actuating member comprises a rod 12 and a stepped disc 13. The rod extends through a circular moulding 18. A compression spring 14 biases the actuating member downwards.

The actuating member 12, 13 can be held in the position shown in Fig. 3 by a pin 15 that extends through a radial bore in rod 12. The pin rests on the moulding 18 and extends into a further moulding 19. Moulding 18 has a camming surface on which the pin rests so that rotation of the rod 12 causes axial movement of the actuating member. One end of the lanyard 85 has a nipple on it (not shown) which engages a recess in the periphery of the moulding 19. A sliding stop (not shown) on the lanyard abuts the outside of the operating head. A further safety pin 16 (not shown in Fig. 3) extends through a further bore 17 in rod 12.

The cylinder valve 30 comprises a threaded portion 31 for screwing into the cylinder 80 and a pick up tube 70. The cylinder valve has an inlet duct 32 and an outlet duct 33. The cylinder valve contains a cutter mechanism 34.

A metal disc 35 is held between the inlet duct 32 and the cutter mechanism by a screwed ring 45. The disc is a bursting disc, is ferromagnetic and is preferably nickel.

The upper part of the cylinder valve has a flange 50.

The cutter mechanism 34 comprises an externally threaded block 36 containing an axially movable cutter member 37.

A compression spring 38 acts on a washer 39 that is screwed to the cutter member to bias the cutter member away from the disc 35. A flexible, permanent magnet 40 is contained in the cutter member. The cutter member is cylindrical and hollow in its lower part. The bottom of the member has a cutting edge 41. The cutting edge member is circular with a gap around its circumference.

The bottom of the cutter member is conical in shape with the cutting edge on the outside of the member. A number of bores 43 extend radially through the hollow portion of the cutter member. There is an annular gap around the cutter member in the vicinity of the bores 43. An elastomeric 0 ring 44 is positioned between the cutter member and the block 36, in a flange in the block, and a further elastomeric 0 ring 47 is positioned between the block and the cylinder valve 30.

To assemble the release valve the metal disc 35 is fitted to the screwed ring 45 and retained by locally deforming it into the groove on the nose of the ring. This assembly is inserted and screwed into the valve body 30. The cutter mechanism 34 is assembled by sliding the cutter member 37 through the threaded block 36 trapping the seal 44 in position. Bias spring 38, washer 39 and a central screw are fitted to retain the cutter member. This subassembly is screwed into the valve body 30. The nose of the cutter member enters the bore of the threaded ring so ensuring a smooth flow path for fluid when the disc is ruptured. The operating head 10 is then assembled. The housing is formed as an upper and lower part. The moulding 18 is positioned in a recess in the top of the lower part. Projections (not shown) on the moulding prevent it from turning in the recess. The actuating member 12, 13 is then passed through the lower part and the moulding 18, against the force of the spring 14 which is positioned between the stepped disc 13 and the lower part of the lower part of the housing. The lower part and moulding both contain a radial slot (not shown) which allows the pin 15 to pass through these components. The actuating member is then twisted so that the pin 15 sits on the camming surface of the moulding 18.

The moulding 19 is then fitted to the upper part of the housing. The moulding 19 can rotate in the upper part but a protrusion on the moulding, which moves in a groove in the upper part, limits its rotation.

Pin 15 engages a radial slot in the moulding 19. The lanyard 85 extends through an aperture in the upper part and the nipple is positioned in said peripheral recess in the moulding 19. The lanyard extends along a circumfer ential groove around part of the moulding 19. The upper and lower parts of the housing are then joined and the safety pin 16 is inserted.

To seal the interior of the operating head 10 when assembled to the valve elastomeric O-rings (not shown) are fitted between the two parts of the housing and at the joint between the valve flange 50 and operating head flange 11. The lanyard 85 is sealed to the upper part by an elastomeric spherical component (not shown) which is pulled into a tapered cylindrical bore in the upper part when the lanyard is in the stored condition.

The flange 11 on the operating head 10 is then butted onto the flange 50 on the cylinder valve 30 and the operating head and cylinder valve joined by a clamp 60.

The relative angular position of the outlet port on the valve 33 and the axis of the lanyard can be adjusted to suit the particular installation before the clamp is fully tightened.

The release valve operates to release compressed gas in the cylinder 80 so that it flows out of the outlet duct 33 in the cylinder valve 30. This is achieved by puncturing the disc 35 with the cutter member 37.

The release valve is assembled with its components in the position shown in Fig. 3. Firstly, the safety pin 16 is removed. The safety pin prevents the release valve being accidentally actuated. The release valve is actuated by pulling the lanyard 85 with a load of 65N or more. This rotates the moulding 19 which turns the rod 12. The pin 15 rises up the camming surface on moulding 18 until it can fall through the radial slots in the moulding 18 and the lower part of the housing 10. The spring 14 forces the actuating member downwards so that it strikes the top of the cutter member 37 and forces it downwards, against the action of spring 38. The cutting edge 41 cuts through the metal disc 35 and releases the gas in the cylinder.The cutting edge is configured so that it cuts the disc close to the edge of the inlet port 32, thereby minimising flexing of the disc during cutting and minimising the energy necessary to cut through the disc. The shape of the cutting edge causes a portion of the disc to remain intact which then acts as a hinge on which the disc swings. After the lanyard has rotated moulding 19 to energise the cutter, further travel allows it to pull free from the operating head.

Due to variation of environmental conditions the temperature of the equipment will cause a variation of developed pressure inside the cylinder 80. The behaviour of the cut disc is dependent upon the pressure in the cylinder at the time of operation. At low pressures, say 50 bar, the hinge has sufficient strength to retain the disc 35. After operation the disc is still fixed to the annular portion under the screwed ring 45. As the internal pressure increases there is more energy in the discharging gas and this will eventually be enough to break the hinge. When this occurs the disc is trapped inside the hollow portion of the cutter member 37. The diameter of the cut disc is slightly larger than the bore of the hollow portion of the cutter member and so the disc has to deform as it is driven up the cutter member.The disc is curled up as it is forced inside the hollow in the cutter member. At high pressure this curled disc is forced against the magnet 40 and retained there. The bores 43 are sized to prevent the curled disc being forced out of the cutter member and into the outlet duct 33.

When the disc 35 is punctured gas flows up the cutter member 37, through the radial bores 43, and into the outlet duct 33. The escaping gas passes along the hose 90 into the liferaft.

When the release valve is actuated the cutter member 37 engages a recess 46 in the screwed ring 45, but as soon as the gas pressure acts on the cutter member it returns to the position shown in Figs. 3 and 4. In this position the "0" ring 44 prevents gas passing up the outside of the cutter member into the operating head 10.

During storage and transport before operation the cutter assembly 34 will be subjected to vibration and shock loads, these must not cause the cutter member 37 to contact the disc 35. Any contact could damage the disc and cause a premature, unscheduled release of gas. The spring 38 exerts an axial threshold load biassing the cutter member away from the disc. The load for this spring is chosen to give protection against the maximum shock level specified for any application.

To augment the discharge rate at the lower temperatures the cylinder can contain a charge of an inert nonliquefiable gas (e.g. nitrogen) which maintains a higher pressure at the low temperature than the carbon dioxide vapour pressure.

The release valve has a number of advantages over known devices. The release action is effectively instantaneous and the force required to activate the valve is relatively small.

As the cutter member is hollow this maximises the gas flowrate through the valve. The shape of the cutting edge 41 maximises the flow area.

The design of the flowpath through the release valve minimises solidification of the discharging gas. The release valve described can operate satisfactorily at temperatures as low as -30 C.

The energy needed to puncture the disc 35 is low because the energy in the compressed gas also acts to hold the disc under tension.

The design of the cutter employed in the valve just described was chosen in order to open up the largest possible area in the sealing diaphragm therefore maximising the flow of CO2, and giving the most rapid inflation of a liferaft chamber. This is particularly important at low temperature (-300C) when the CO2, is liquid and the vapour pressure is at a minimum (approximately 13 bar).

The valve uses the gas pressure to force back the cut diaphragm, bending the diaphragm material at the "hinge" which is formed by the cut out in the annular cutter.

Thus the force developed by the gas acting on the cut diaphragm has to overcome the resistance offered by the hinge material plus frictional and other forces caused by the geometry of hinging the cut disc back inside the hollow cutter. The diaphragm, when cut by the outside edge of the cutter (nominally 8mm dia), had to be forced by the gas pressure into the internal conical form of the form of the cutter which reduced in diameter from approximately 8mm to 6mm. Although this action could be consistently and reliably performed at high pressure, there was insufficient force developed at low pressure to do this reliably with a consistent wide opening of the cut disc aperture, particularly under the case where CO2 only without N2 padding was employed in the gas cylinder and under low temperature condition (-300C).

A first modification illustrated in Figs. 5 and 6 helps to overcome this problem by using the hollow annular cutter 51 still employing the cut out to form the hinge) but with the cutting edge 52 formed by an external rather than an internal conical section. This then allows the internal bore 53 of the cutter to be parallel, thereby offering minimum resistance to the disc cut in the diaphragm as it is pushed back about its hinge by the low gas pressure.

The external cone surface 54 on the cutter 51 involves moving the cutting edge 52 further away from the point at which the diaphragm 35 is supported by being clamped between the diaphragm holder and the cylinder valve sealing face. This results in less stiffness of the diaphragm during the cutting action, with correspondingly greater loss of operating spring energy, i.e. a less efficient cutting system with a lower reserve energy margin from the operating head spring.

In order to overcome this problem an annular support ring 55 is incorporated. This is manufactured in the same grade of stainless steel as the cutter and is screwed into the valve body and rivetted in place. Before rivetting in place the support ring is adjusted so that it protrudes (dimension k) beyond the valve diaphragm sealing face by 0.5/0.4mm. This setting ensures that the support ring protrudes into the concave cavity of the diaphragm 35 which is formed when the gas pressure is applied and is close to the diaphragm (see Fig.6). When the cutting operation takes place the cutter impacts on the diaphragm and pushes it on to the support ring. The support ring prevents further movement of the diaphragm, in effect significantly increasing its stiffness.Thus the cutter dissipates its energy in straining the diaphragm material to the breaking point i.e. performing the cutting action rather than moving the whole diaphragm against the gas pressure and wasting energy. The cutter edge and support ring do not however directly shear the diaphragm.

As can be seen particularly in Fig.6, the cutting edge 52 is not totally sharp, but has a small annular front surface 56. Further, the front outer surface of the support ring 55 is radiussed at 57. Moreover, there is a small annular clearance (dimension m) between the two surfaces which engage the diaphragm. The effect of these measures is that the diaphragm 35 is stretched over the radius 57 before it breaks so as to form a downwardly depending lip 58 around the edge of the hinged flap 59. A break 62 in the cutting edge 52 allows the formation of the hinge 63. This is illustrated in Fig.7 which shows the diaphragm turned by 900 compared with its position in Figs 5 and 6. The degree to which this lip appears depends upon how soon the diaphragm material ruptures, which depends on the upward pressure of the gas. There is a smaller lip formed with higher gas pressure, and vice versa.

This has the advantageous effect that for lower gas pressure, the gas flow 61 has a larger lip 58 against which to react, and thus ensures that the flap 59 is opened sufficiently wide to meet the necessary flow rate specifications down to about 3 bar gas pressure.

The features described with reference to Figs. 5 to 7 may be used individually, or in combination as described.

Each contributes to an improved performance. In combination, they provide a release valve which comfortably exceeds all the evolved criteria for use in inflatable craft for emergency use at sea. In particular, the embodiment of Figures 5 to 7 has been found to operate reliably at very low vapour pressures (CO2 at-300C) and still produce a fully open unrestricted valve.

The disclosures in British patent application no.

94/13686.8 from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims (7)

CLAIMS:

1. A gas release valve comprising a valve body adapted to be connected to a source of compressed gas and further adapted to be connected to an inflatable body, a gas flow path through the valve body from the source of compressed gas to the inflatable body, diaphragm means sealing the flow path, cutter means operable to rupture the diaphragm means1 valve release means, and means to actuate the cutter means, wherein the cutter means comprises a blade of generally cylindrical form with a cutting edge at one annular end, and a correspondingly annular shaped support ring against which in operation the cutting edge pushes the diaphragm means before it ruptures, the ring lying radially within the cutting edge.

2. A gas release valve according to claim 1, wherein annular support ring includes a rounded outer annular surface against which the diaphragm means is pushed during cutting.

3. A gas release valve according to claim 1 or 2, wherein the annular support ring has an outer radius smaller than the inner radius of the blade of the cutter means so as to be radially spaced therefrom.

4. A gas release valve according to claim 3, wherein the radial spacing is substantially the same as a thickness of the diaphragm means.

5. A gas release valve according to any preceding claim, wherein the annular end of the blade has an inner surface of substantially uniform radius.

6. A gas release valve according to any preceding claim, wherein the annular end of the blade has an acute angle cross-section which has an outer surface which increases in radius progressively away from the annular end.

7. A gas release valve substantially as hereinbefore described with reference to and as illustrated in Figures 5 to 7 of the accompanying drawings.