GB2110358A

GB2110358A - Apparatus for discharging pressurised containers

Info

Publication number: GB2110358A
Application number: GB08230855A
Authority: GB
Inventors: John Walter Rilett
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-11-07
Filing date: 1982-10-28
Publication date: 1983-06-15
Also published as: IT8249415A0; EP0093130A1; JPS58501870A; WO1983001669A1; IT1148450B; GB2110358B; ZA827886B

Abstract

Apparatus for discharging a pressurised container (61) in which a hollow body (10) has internal bore means (20, 25) and in which closure opening means, e.g. a hollow pin (53) is mounted on piston means (15) slidably located in part of the bore means, e.g. in a piston cylinder (25); there being a passage (150) which extends from the pin to the opposite side of the piston means so that the initial release of gas passes through the piston means and drives the piston means towards the container to sealingly clamp sealing abutment means (54) against the end of the container around the pierced closure (64) of the container. <IMAGE>

Description

SPECIFICATION Apparatus for discharging pressurised containers This invention concerns improvements relating to apparatus for discharging pressurised containers, such as carbon dioxide bulbs and gas cylinders.

Apparatus is known for use in discharging compressed gas cylinders of the kind which are closed by closure means in the form of a frangible diaphragm seal, which apparatus comprises hollow body means usually having an inlet end portion remote from an outlet end portion; closure opening means associated with the inlet end portion and comprising a hollow piercing pin usually located at the axis of a mouth; and the apparatus is provided with or is associated with screw means to enable a nose of the container to be driven into the mouth so that the pin pierces the frangible diaphragm seal of the container to allow the contents of the container to flow into the body via the pin. Such apparatus is hereinafter referred to as being "of the piercing kind" for the sake of brevity.

In some known apparatus of the piercing kind the pin starts to puncture the diagram seal as the nose enters the mouth, and then the pin slides through the puncture until the nose reaches a mouth seal around the pin at the base of the mouth. This piercing kind of apparatus suffers from two main disadvantages in that gas can escape during the interval between the seal being punctured and the nose making sealing engagement with the mouth seal, and in that the screw means, which comprises a holder having a thread which cooperates with a thread on the body to produce the necessary thrust upon the holder being rotated, can be stiff and slow to operate. If the thread pitch is increased to increase the rate of axial movement of the container relative to the pin, the stiffness of operation of the screw means is increased undesirably.

Apparatus is also known for use in discharging compressed gas cylinders of the kind which are closed by closure means in the form of a valve which is openable from a sealing condition by depressing a valve spindle, which apparatus comprises hollow body means usually having an inlet end portion remote from an outlet end portion; and closure opening means usually associated with the inlet end portion and comprising a pin located at the axis of a mouth; which apparatus is provided with or is associated with screw means to enable a nose of the container to be driven into the mouth so that the pin depresses the spindle to allow the contents of the container to flow into the body. Such apparatus is hereinafter referred to as being "of the valve releasing kind" for the sake of brevity.

Known apparatus of the valve releasing kind suffers from the disadvantage that, as the nose is driven into the mouth, the pin starts to open the valve before the nose effectively engages a seal in the mouth, thereby allowing gas under pressure to escape from the mouth. Sometimes such escaping gas will make a violent hissing noise, which causes alarm to some persons.

Both of said known kinds of apparatus are of a general form comprising:- (a) hollow body means, (b) bore means in said hollow body means, (c) closure opening means associated with said bore means for opening closure means of a pressurised container.

What is needed is means for incorporation into apparatus of this general form which enables the disadvantages of either of the kinds described to be reduced or obviated.

According to the present invention it is generally proposed to operate the closure opening means, e.g. the pin, by piston means slidably located in part of said bore means, e.g. in a piston cylinder, in said body; and to provide a passage from the pin to the opposite side of the piston so that the initial release of gas passes through the piston means and drives the piston means towards the container to sealingly clamp sealing abutment means against the container, e.g. the nose or end of the container, around the opened closure means of the container.

According to the present invention there is provided apparatus, for discharging pressurised containers, which apparatus is of the general form mentioned above and which apparatus is characterised in that it comprises operational means for complete opening of, and for preventing undesired leakage from, closure means of a pressurised container, said operational means comprising: (d) piston means slidably located in said bore means to operate said closure opening means; (e) sealing abutment means provided at one side of said piston means around said closure opening means; (f) piston sealing means between said piston means and said bore means; and (g) duct means providing a passage from said closure opening means through said piston to that side of the piston which is remote from said one side.

In use, when the closure opening means opens the closure means, e.g. when the pin initially pierces the diaphragm seal or opens the valve, gas or liquid under pressure passes behind the piston means, either via the closure opening means or around the closure opening means and through the passage to drive the piston means rapidly towards the nose or end of the container until the nose or end of the container is sealingly engaged by the sealing abutment means of the piston means, thus substantially obviating the interval during which gas or liquid can escape and automatically completing the opening operation, e.g. the piercing operation or the valve opening operation.

The apparatus of the invention may comprise screw means preferably actuable to cause the piston means to be moved to abut a seating in said body, so as to clamp the nose or end against the sealing abutment means of the piston means to effect a finai static seal which is not dependent upon gas or liquid pressure to urge the piston means towards the nose or end of the container.

In the case in which the invention is embodied in apparatus of the piercing kind, the closure opening means is preferably in the form of a pin which comprises a conically tapered portion which converges to a tip having a leading face which is inclined at a shallow angle to a plane normal to the pin axis, so that the tip can make a momentary seal with a small portion of the diaphragm seal as the seal is initially pierced, whereby to further reduce leakage and to ensure rapid operation of the piston.

The cone angle of the tapered portion is preferably about 400 pius or minus up to 100, and said shallow angle is preferably about 15 plus or minus up to 5 .

The piston means may define a socket which serves as the mouth concentric with the bore means, and the wall of the socket is preferably grooved to prevent any fiuid which leaks between the pin and the sealing abutment means from blowing or thrusting the sealing abutment means out of the socket.

A portion of the wall of the bore means at the inlet end of the body is preferably grooved or provided with substantially-radial vent holes, to prevent the piston means being blown out of the bore means if the container is removed whilst still under pressure.

The sealing abutment means preferably comprises a resilient seal which is preferably carried by or incorporated into the piston means so as to embrace the tapered portion of the pin, so that the embrace is increased by the taper as the seal is thrust away from the tip, to further reduce leakage.

When applied to apparatus of the valve releasing kind the sealing abutment means is preferably resilient and is preferably arranged to contact the nose or end of the container just before or just as the pin starts to open the valve.

The bore means is preferably provided with pressure relief means, such as grooves, to negate or render inoperative the piston sealing means, forpreventing the piston means from being blown out of the bore means when the container is removed.

The piston means is preferably in the form of a moulding of elastomeric or plastics material which integrally incorporates the piston sealing means, and/or the sealing abutment means, and/or the duct means or part of the duct means.

In the case wherein the piston means serves as a mounting for a separately made sealing abutment means, the piston means may be provided with pressure relief means to prevent the sealing abutment means being blown off the piston means.

The body means may be moulded to incorporate safety means such as an integral burst-disc or other weak spot arranged to fracture when the bore means is subjected to a pressure above or exceeding a predetermined maximum pressure.

In general, the apparatus of the invention has the advantage that, in apparatus of the piercing kind, the diaphragm seal is pierced cleanly so as to minimise the production of fragments, and, in apparatus of the valve releasing kind the valve is opened quickly and fully, and in both cases manual effort is greatly reduced, loss of gas becomes negligible and alarming hissing noises are eliminated.

The apparatus may include an internal filter which is accessible for cleaning or replacement when the piston means is extracted.

It is known to provide apparatus of both kinds with valve means, but due to the high pressures involved said valve means includes a poppet valve member made from metal, and a suitably formed valve seating. Such valve means is expensive to make and can become blocked or jammed for various reasons, e.g. discharge grooves in the valve stem or spindle may become clogged or choked with particles from the gas cylinder.

Experiments with less expensive to produce valve members indicated that plastics material was unsuitable because the pressures involved caused plastics valve members, designed to give an effective seal, to be extruded through the outlet.

What is needed is less expensive but effective valve means for such apparatus.

According to the present invention there is also provided valve means, in apparatus for discharging pressurised containers, comprising a valve member movable within a body of the apparatus, and a closure spring, the body providing an outlet passage and a valve seating co-axial therewith; wherein the valve seating comprises a part conical or chamfered surface which diverges to merge with an annular abutment surface, which abutment surface extends in or close to a first plane perpendicular to the axis of the seating, and which surface is remote from the outlet passage; wherein the valve member is moulded, cast, diecast, machined or formed from a hard plastics material or from metal and comprises a spindle, slidably located in the outlet passage, a valve face which diverges from said spindle to an abutment face, and, remote from the spindle, an extension which projects into the spring; and wherein the abutment face extends in, or close to, a second plane perpendicular to said axis and spaced apart from said first plane when the valve is held closed by said spring.

The valve means of the invention enables the valve seating and valve face to be arranged to give a good seal, whilst the abutment surface and abutment face come into abutment to prevent extrusion of the valve member through the outlet passage when the apparatus is pressurised by gas.

The valve member and body are preferably accurately made, e.g. made to close tolerances, so as to leave clearance therebetween which is sufficiently large for gas flow and sufficiently small to give adequate guidance for the valve member, thereby obviating the need for flutes.

The spring preferably has an end portion which grips the extension on the valve member.

The invention will be described further, by way of example, with reference to the accompanying diagrammatic drawings, wherein: FIGURE 1 shows, in longitudinal cross section, piercing apparatus of the invention, with a CO2 container shown in broken lines; FIGURES 2, 3 and 4 show portions of the piercing apparatus, including piston means, to illustrate three stages of a piercing operation; FIGURE 5 is an enlarged view of a pin form of closure opening means carried by the piston means; FIGURE 6 shows an optional filter of the piercing apparatus; FIGURE 7 shows an enlarged cross-section through a second embodiment of piercing apparatus of the invention; FIGURE 8 is a sectional view of a modification applicable to the second embodiment to convert the piercing apparatus to a valve-releasing apparatus of the invention; and FIGURE 9 is a sectional view of a valvereleasing embodiment of apparatus of the invention.

Referring to FIGURES 1 to 6 of the drawings the piercing kind of apparatus shown comprises moulded hollow body means 10, valve means 13, a filter means 14, piston means 15, and screw means 1 6.

The body means 10 is in the form of a moulded plastics body 10 which is hollow and is internally stepped to define bore means, a narrow outlet passage 20 at an outlet end of the body, a valve seating 21, a filter seating 22, a piston seating 23 and a shoulder 24 for a wide cylinder 25 opening at an inlet 26 of the body. The body 10 has external lugs 11 for grasping by a user of the apparatus, and is moulded to incorporate safety means in the form of an integral bursting disc 27 (FIGURE 1) designed to rupture if a predetermined maximum pressure is exceeded.

The valve means 13, comprises a diecast metal valve member 30 which is urged onto the seating 21 by a spring 31 which reacts against the filter 14. The filter means 14 comprises a porous or perforate body and locates in an inner end part of the piston means 1 5.

The piston means 1 5 is an assembly which comprises an internally and externally stepped hollow moulded piston 50; an-external resilient piston ring 51 which is located in the cylinder 25 between the shoulder 24 and a shoulder 52 on the piston 50 to serve as piston sealing means; closure opening means in the form of a hollow needle or pin 53 secured in the piston 50; and sealing abutment means in the form of a resilient socket seal 54 located around the pin 53 at the base of a hollow socket 55 defined by an extension 56 of the piston so as to serve as a guiding mouth. The hollow interior of the piston 50 serves as duct means which provides a passage 150 from the hollow pin to the left hand side of the piston 50.

Referring also to FIGURE 5 the pin 53 has a conically tapered portion 57 which converges to a tip 58 having a face 59. The cone angle A is 400; the face 59 iies at an angle B of 15 to a plane C normal to the axis D common to the pin 53, piston 50, cylinder 25 and inlet end 26.

The seal 54 is internally tapered to embrace the portion 57 in the as assembled condition of the piston assembly.

The screw means 1 6 comprises a holder 60 for the CO2 container cylinder 61, which holder 60 has an internal thread 62 at one end which thread engages an external thread 63 on one end 26 of the body 10.

In use, the holder 60 can be detached from the body 10 to allow the cylinder 61- to be inserted, and then re-attached in known manner so that a closure in the-form of a frangible diaphragm seal 64 at a nose 65 of the cylinder 61 is brought proximal to the pin 53, the socket 55 serving to align the nose 65 with the axis D as shown in FIGURES 1 and 5 respectively. Thereafter, the holder can, quite easily, be further rotated to drive the container axially towards the body 10 until the cylinder 61 reaches the position whereat the tip 58 has just penetrated the seal 64.In this position (FIGURE 2) the tip 58 makes, momentarily, a sufficiently effective seal with the remainder of the diaphragm seal 64 around the small puncture to constrain the CO2 to flow into the pin 53 so as to pass through the passage 150 into the body 10 to pressurise the interior of the body and the cylinder behind the piston ring 51.

This pressurisation drives the piston assembly 15 bodily towards the cylinder 61 at high speed so as to drive the conical portion 57 to abut the seal 54 and to cause the seal 54 to abut, to be compressed by and to sealingly engage the nose 65, as shown in FIGURE 3.

In practice, the position shown in FIGURE 3 arises a fraction of a second after the FIGURE 2 position is reached, without any significant manual effort being applied to the holder. The effectiveness of the seal 54 is enhanced by the seal being forced to expand radially as it is forced against the tapered portion 57.

The combination of rapid penetration and immediate sealing effectively prohibits leakage of the CO2, the piston means 1 5 in combination with the sealing abutment means 54, the piston sealing means 51 and the duct means 1 50 thus serving as operational means responsive to gas or liquid pressure, provided by the initial opening of the closure means, for actuating the closure opening means 53 to complete the opening of the closure means 64 and for sealingly engaging the container 61.

It is not normally necessary for the holder to be further rotated, but in the event that the holder is further rotated it will push the piston 50 back into its seating and hold the seal 54 in a compressed state, as shown in FIGURE 4, so as to relieve the piston ring and to maintain a sealed condition in the event of the pressure in the body being released by opening the valve 13 (e.g. by a mechanism known per se).

Access to the filter 14 can be facilitated by unscrewing the holder before the cylinder 61 is exhausted so that the pressure in the body causes the piston assembly 1 5 to follow the cylinder 61 until the piston ring reaches pressure relief means in the form of grooves 70 formed in the peripheral wall of the cylinder 25 thereby allowing the pressure to be released. (This release of pressure also prevents the piston assembly being "shot" by gas pressure out of the body if the holder is accidentally removed.) When the holder is removed the extension 56 can be grasped to draw out the piston assembly and the filter 14.

The wall of the socket 55 is provided with similar pressure relief means in the form of grooves 71, so as to provide a vent path for any gas which escapes between the pin and the seal 54, whereby to prevent the seal 54 being blown out of the socket.

As shown in FIGURE 6, the filter 14 is preferably formed to serve as a miniature cyclone filter 40 in which the gas is forced to rotate at high speed as it passes into the filter, and thereafter to move towards the axis D before passing through a narrow axial discharge passage 41, to cause foreign matter to be flung to the peripheral wall 42 of the filter.

Although piston means generally of the form described is preferred for some purposes, it may be possible, for simplifying the apparatus to reduce cost, to omit the extension 56 and optionally arrange the seal 54 to engage the cylinder 25, so that the socket 55 is omitted to leave the cylinder 25 to provide a large mouth, and optionally the seal 54 or cylinder 25 may be modified to serve as a socket or guide means for the nose 65, or a separate guide may be provided to align the nose with the axis D of the mouth.

A simplified low cost form of the invention is shown in FIGURE 7 and in this Figure the same reference numerals are used for those parts which are the same as parts in the preceding Figures whereas modified parts are indicated by reference numerals with the suffix A.

Referring to FIGURE 7, the apparatus shown is of the piercing kind and comprises a moulded body 10A, the valve means 13A, piston means 15A, and screw means 16A.

The moulded body 1 OA is hollow and is internally stepped to define bore means comprising a narrow outlet passage 20A at an outlet end of the body, a valve seating 21, a piston seating 23 and a shoulder 24 for a wide piston cylinder 25A which adjoins a socket 55A opening at an inlet end 26A of the body. The body has external ribs 11 A, and a bursting disc 27A.

The piston means 15A carries closure opening means in the form of the hollow needle or pin 53.

The pin 53 is secured in an internally and externally stepped hollow moulded piston 50A.

The piston 50A has an integral piston sealing means comprising a resilient piston skirt ring portion 51 A (sealingly engages the cylinder 25A adjacent the shoulder 24); and has an integral sealing abutment means in the form of a seal 54A located around the pin 53 so as to constitute a base of the hollow socket 55A which serves as a guiding mouth.

The pin 53 is as hereinbefore described with reference to FIGURE 5.

The end portion of the piston forming the seal 54A is internally tapered to embrace part of the portion 57 of the pin in the as assembled condition of the piston means, and the opposite end portion of the piston is provided with radial grooves 12.

The screw means 1 6A comprises an internal thread 63A within the socket 55A for engagement by an external thread 62A on a nose 65A of a CO2 container cylinder 61A.

In use, the nose end 65A of the cylinder 61 A is inserted into the socket 55A, and is then rotated in known manner to bring a frangible diaphragm seal 64 at the nose end 65A proximal to the pin 53, the socket serving to align the nose 65A with the axis of the pin and socket as shown in FIGURE 7.

Thereafter, the body 1 OA or gas cylinder 61 A can, quite easily, be further rotated to cause the tip 58 to puncture the seal 64 as explained hereinbefore with reference to FIGURE 2, to cause the CO2 to flow into the pin 53 so as to pass through the piston 50A into the body 1 OA to pressurise the bore means in the interior of the body and to pressurise the cylinder behind the piston ring portion 51 A via the grooves 12.

This pressurisation drives the piston assembly 15A bodily towards the gas cylinder 61 A at high speed so as to drive the conical portion 57 into the seal 64 and to cause the seal 54A to be compressed by and to sealingly engage the nose 65A, a fraction of a second after the seal 64 is punctured.

As described hereinbefore, the combination of rapid penetration and immediate sealing effectively prohibits the leakage of the CO2.

It is preferable for the piston 50A to be formed from an elastomeric material, e.g. the material sold by ICI Ltd under the name HYTREL (Registered Trade Mark) so that the seal 54A and the piston ring 51A can be integrally incorporated in the piston 50A.

The pressure relief means may comprise ports 70A which are formed in the wall of the cylinder 25A as shown in broken lines, so that if the cylinder 61A is unscrewed before the pressure is exhausted the pressure in the body does not cause the piston assembly 15A and the gas cylinder 61 A to be driven outwards beyond the point at which the piston ring reaches and uncovers the pressure relief ports 70A. Alternatively the grooves 70 may be provided in the cylinder wall.

In both of the forms described hereinbefore the valve means 13 and 1 3A are formed so that, as shown diagrammatically in FIGURE 7, the valve member 30 comprises a cylindrical spindle 32 slidable in the passage 20A (or 20), an extension 33 which is gripped by the first one or two turns of the spring 31, and a tapered or frusto-conical valve face 34 which diverges to merge with an abutment face 35 which extends in a plane E perpendicular to the axis D. The valve seating 21 comprises a chamfered or part conical surface 36 which diverges from said passage to merge with an abutment surface 37 which is disposed in a plane F.The largest diameter of the frusto-conical face 34 is greater than that of the surface 36 so that, in the condition in which the valve is closed by the spring, the planes E and F are spaced apart as shown, but when the apparatus is pressurised by gas, the valve member is prevented from being extruded through the outlet passage by abutment of the face 35 with the surface 37. Clearances are provided around the spindle 32 and a body part 38 of the valve member for gas flow.

Both forms of the apparatus described may be constructed as apparatus of the valve-releasing kind, by suitably altering the dimensions of the apparatus to suit the valved gas cylinders and by substituting closure opening means in the form of a valve-releasing pin for the piercing pin, as illustrated diagrammatically in FIGURE 8.

In the portion of the valve-releasing apparatus shown FIGURE 8 the piston means 15A is provided with a valve-releasing pin 80 which is substantially the same as the pin 53 except in that the tip 81 has an end face 82 in a plane normal to axis D, and in that the tip 81 is transversely slotted to provide openings 83 to allow gas to enter the pin when the end face 82 abuts the valve actuating spindle 84 of a valved gas cylinder 85.

The pin 80 and seal 54A are arranged so that the pin just contacts the spindle 84 to start to open the valve as the cylinder nose 86 contacts the seal 54A. As soon as gas leaves the cylinder 85 the piston assembly 1 5A is driven to the cylinder 85 as hereinbefore explained, and causes the pin 80 to open fully the cylinder valve.

Referring to FIGURE 9, the invention may be applied to valve-releasing apparatus having closure opening means in the form of a solid pin 80B which is located in a piston means 15B similar to the piston means 15A except in that the duct means includes internal grooves 90, which grooves 90 are provided in the piston means around the pin 80B to allow gas to pass through the piston means 15B, and in that the sealing abutment means is a separate elastomeric seal 54B having a central aperture which providers a clearance around the pin 80B for gas to enter the grooves 90. Other parts common to the piston assemblies 1 5A and 15B are indicated by the same reference numbers.

This apparatus is constructed as an adaptor which is adapted to be joined to the first embodiment of apparatus (as in FIGURE 1) by means of an internally-threaded extension 91 so that a concentric extension 92 (FIGURE 9) abuts the seal 54 (FIGURE 1) and receives the tip 58 of the pin 53.

An integral bursting disc 27B is moulded into the adaptor body 93, and a fixed mouth piece 94 is permanently secured in the body 93 to define an internally threaded socket 55A at the inlet end of a large diameter piston cylinder 25B so as to retain the piston means 15B in the piston cylinder 25B.

The pin means 15B functions in a manner equivalent to the operation of the piston means 15A to effect a seal with and open fully the valve of the gas cylinder 85.

It will be readily appreciated that the apparatus of the invention can be constructed in many forms for use in opening various types of cylinders or other apparatus containing gas or liquefied gas at very high pressure, and that the invention is not confined to the precise details of the foregoing example or any particular combination or combinations of the various features incorporated in these examples.

For instance, a filter may be provided in all embodiments, including apparatus constructed to serve as an adaptor.

In the valve means, the inclinations or cone angles of the valve surface and valve face may be varied to suit the constructional materials employed, or said surface and/or said face may be curved or flared. The abutment face and surface may be inclined slightly to the respective planes E and F.

In apparatus of thevalve-releasing kind the pin may be of plastics material and may be moulded integrally with or into the piston moulding.

Claims

1. Apparatus, for discharging pressurised containers having closure means, which apparatus comprises: (a) hollow body means (10, 1 OA, 93), (b) bore means (20, 20A, 25, 25A, 2SB) in said hollow body means, (c) closure opening means (53, 80, SOB) associated with said bore means for opening closure means (64, 84) of a pressurised container (61,61A, 85); said apparatus being characterised in that it further comprises:: (d) piston means (15, 15A, 15B) slidably located in said bore means to operate said closure opening means; (e) sealing abutment means (54,54A,54B) provided at one side of said piston means around said closure opening means; (f) piston sealing means (51,51A) between said piston means and said bore means; and (g) duct means (1 50) providing a passage from said closure opening means through said piston to that side of the piston which is remote from said one side.

2. Apparatus as claimed in Claim 1, wherein bore means is provided with pressure relief means (70, 70A) to negate or render inoperative the piston sealing means, for preventing the piston means from being blown out of the bore means.

3. Apparatus as claimed in Claim 1, wherein the piston means comprises an elastomeric moulding (1 5A) which integrally incorporates the piston sealing means (51A) and the sealing abutment means (54A).

4. Apparatus as claimed in Claim 1 further comprising filter means (14, 40).

5. Apparatus as claimed in Claim 1, wherein the body means is moulded to incorporate safety means (27, 27A, 27B) arranged to open when the bore means is subjected to a pressure above or exceeding a predetermined maximum pressure.

6. Apparatus as claimed in Claim 1, wherein the closure opening means comprises a hollow piercing pin (53) seated in the piston means; wherein the pin comprises a conically tapered portion (57) which converges to a tip (58) having a leading face (59) which is inclined at a shallow angle to a plane C normal to the pin axis D.

7. Apparatus as claimed in Claim 6, wherein the cone angle of the tapered portion is 400, plus or minus up to 100, and said shallow angle is 1 50 plus or minus up to 5 .

8. Apparatus as claimed in Claim 6, wherein the sealing abutment means comprises a resilient seal (54) which embraces the tapered portion (57) of the pin, so that the embrace is increased by the taper as the seal is thrust away from the tip during opening.

9. Apparatus as claimed in Claim 1, wherein the piston means (1 5) serves as a mounting for a separately made sealing abutment means (54), and wherein the piston means is provided with pressure relief means (71) to prevent the sealing abutment means being blown off the piston means.

10. Apparatus as claimed in Claim 1 comprising valve means (13, 1 3A), said valve means comprising a valve member (30) movable within said bore means, and a closure spring (31), the body means providing an outlet passage (20, 20A) and a valve seating (21) co-axial therewith; wherein the valve seating comprises a part conical or chamfered surface (36) which diverges to merge with an annular abutment surface 37, which abutment surface extends in or close to a first plane F perpendicular to the axis D of the seating, and which surface is remote from the outlet passage (20 20A); wherein the valve member comprises a spindle (32), slidably located in the outlet passage, a valve face (34) which diverges from said spindle to an abutment face (35), and, remote from the spindle, an extension (33) which projects into the spring; and wherein the abutment face (35) extends in, or close to, a second plane E perpendicular to said axis and spaced apart from said first plane when the valve is held closed by said spring.