GB2292785A - Flow Control Valve Assembly - Google Patents

Abstract

A flow control valve assembly for attachment to a gas cylinder has a valve body (10) with an inlet connector (12) for attachment to the cylinder and an outlet connector (28) for attachment to a system to be pressurised with gas from the cylinder. A valve seat (16) and manually operable valve member (20) control the flow of gas in a flow passage interconnecting the inlet and the outlet connectors (12 and 28). A pressure retaining device (40) mounted in the valve body (10) serves to close the flow passage when the pressure in the latter falls below a predetermined value and includes a closure member (42) disposed in a recess (30) in the valve body (10) opening into an intermediate region (34) of the flow passage leading to the outlet connection (28). The closure member (42) has mutually spaced, smaller and larger diameter regions (44 and 46) and is biassed by a spring (47) into a closed position, in which the smaller diameter region (44) engages a sealing surface (32) which extends around the flow passage from an open position, in which the smaller diameter region (44) is disposed within the recess (30) and out of the flow passage. The larger diameter region (46) is sealingly and slidably engaged with a wall of the recess (30). The intermediate region (34) may be formed by milling or electrochemical machining. A method of manufacturing a plurality of valve bodies is also disclosed. <IMAGE>

Description

FLOW CONTROL VALVE ASSEMBLY This invention relates to a flow control valve assembly and is more particularly concerned with a flow control valve assembly for attachment to a gas cylinder, e.g. a gas cylinder containing carbon dioxide or a mixture of carbon dioxide and nitrogen.

Known flow control valve assemblies for pressurized gas cylinders comprise a valve body having an inlet connector including an externally screw-threaded and tapered sleeve which is screwed into a standard internally threaded hole at the end of the gas cylinder. The body of such a valve assembly further includes an outlet connector which may be either of two standard types so as to enable ready attachment by means of a standard fitting to a system to be supplied with pressurized gas from the cylinder. The body further includes a flow passage providing communication between the inlet and the outlet connectors, a valve seat in the flow passage, and a moveable valve member mounted in the body for movement towards and away from the valve seat in order to control the flow of gas in the flow passage in use.Usually, such moveable valve member is manually operated by means of a rotary hand wheel carried by the valve assembly.

In the above description, the inlet connector is that which is attached to the gas cylinder and the outlet connector is that which is attached to the system to be supplied with pressurised gas in use. However, it will be appreciated that, during re-filling of the cylinder, the flow of gas will be reversed. Thus, references hereinafter to "inlet connector" and "outlet connector1 are to be interpreted in relation to the purpose served by these connectors when the valve assembly is being used to control the supply of gas from the cylinder.

Particularly when the flow control valve assembly is being used with a system for dispensing liquids such as alcoholic and non-alcoholic beverages, there is a risk of liquid leaking back along the gas supply system and into the gas cylinder, particularly when the pressure in the gas cylinder becomes low. This is obviously undesirable since it can cause corrosion of the cylinder and also hygiene problems. In order to overcome these problems, it is known to provide in the valve assembly a pressure retaining device which serves to seal the flow passage automatically when the pressure in the gas cylinder falls below a predetermined pressure (typically two bar.). Various types of pressure retaining device are known and the detailed design of these depends inter alia upon the type of standard outlet connector utilised on the valve assembly.However, they generally comprise a closure member which is resiliently urged by a spring into a closed position (in which the closure member is in sealing engagement with a surface) so as to close the flow passage but which is urged away from the closed position into an open position when the effect of differential pressure acting on the closure member in opposition to the spring exceeds that of the spring.

One form of standard outlet connector comprises an externally screwthreaded sleeve upon which a standard internally screw-threaded fitting is engaged when the gas cylinder is connected into the system to be supplied with gas. With such a design, the pressure retaining device can take the form of a pre-assembled cartridge-type device which is disposed as a unit into the outlet connection and screwed into position, the outlet connection having an internally screw-threaded bore to accept the pressure retaining device.

Another form of standard outlet connector is internally screw-threaded for connection to a standard externally screw threaded fitting. With such a design, the use of such a cartridge-type pressure retaining device is not generally possible because there is a risk of it becoming un-screwed when a standard fitting which has previously been introduced into the outlet connector is un-screwed therefrom during gas cylinder replacement. Accordingly, an alternative form of pressure retaining device is known which is inserted into the opposite end of the valve body from the outlet connector and cooperates with an angled drilling in the valve body. The closure member and spring of the device are held in place by a retaining nut which seals said opposite end of the valve body.

It will therefore be appreciated that two separate designs of valve body and of pressure retaining device are required to satisfy the demand for flow control valve assemblies having the different standard outlet connectors.

In some of these known designs of pressure retaining device (see, for example, US 4341245 and EP-A-0386740), the closure member is disposed within the flow passage between the inlet and the outlet connections in both its open and its closed positions and thereby constitutes a restriction to flow of gas between the inlet and the outlet connectors. This can provide problems during re-filling of the gas cylinder since there is a need to fill the gas cylinder as quickly as possible for reasons of economy. There is a demand for the gas cylinder to be re-fillable rapidly. This can cause an undesirably high increase in temperature within the flow control valve assembly during re-filling, particularly when re-filling using a liquefied gas such as liquefied carbon dioxide.

In other known designs of pressure retaining device, this problem is reduced by designing the closure member so that it is moved out of the direct flow path between the inlet and outlet connectors when in its open position. This is achieved by mounting the closure member and spring in a hollow in an externally screw-threaded plug sealingly engaging in an end of an internally screw-threaded recess which is not in the flow passage as such but which communicates with the flow passage and is aligned with the outlet connection. The closure member is stepped and provided with o-ring seals so as to define spaced smaller and larger diameter regions which therefore have smaller and larger effective areas.The bring seal on the larger diameter region is sealingly and slidably engaged with a peripheral surface of the hollow in the plug whilst the o-ring seal on the smaller diameter region is engageable with the sealing surface in the flow passage. There is an angled drilling in the body which is disposed adjacent the sealing surface on the opposite side thereof to the outlet opening and which defines an intermediate region of the flow passage between the sealing surface and the inlet connection.

With such an arrangement, as the pressure within the intermediate region rises when the moveable valve member is manually opened during normal use of the valve assembly, this pressure acts on both smaller and larger diameter regions of the closure member, but the net effect is to act thereon in opposition to the spring and eventually move the closure member back within the hollow in the plug so that no part of the closure member lies in the direct flow path from the intermediate region to the outlet connection. During re-filling of the cylinder, a specially adapted refilling nozzle is engaged with the outlet connection and has a portion which bears against the closure member to urge it into its open position.

However, even with such a design, there is still an unacceptably high flow restriction, particularly when it is required to re-fill using a liquefied gas.

It is an object of the present invention to provide a novel flow control valve assembly which can enable the above disadvantages to be obviated or mitigated.

According to one aspect of the present invention, there is provided a flow control valve assembly for attachment to a gas cylinder, said assembly comprising a valve body having an inlet connector adapted to be attached to a gas cylinder and an outlet connector adapted to be attached to a system to be pressurised with gas from the cylinder in use; a flow passage in the valve body providing communication between the inlet and the outlet connectors; a valve seat in the flow passage; a moveable valve member mounted in the body for movement towards and away from the valve seat in order to control the flow of gas in the flow passage in use; and a pressure retaining device mounted in the valve body and arranged to close the flow passage in use when the pressure in the flow passage falls below a predetermined value, the pressure retaining device including a closure member disposed in a recess in the valve body, the recess opening into an intermediate region of the flow passage leading to the outlet connection, the closure member having mutually spaced, smaller and larger diameter regions and being moveable between a closed position in which the smaller diameter region engages a sealing surface which extends around the flow passage and an open position in which the smaller diameter region is disposed within the recess and out of the flow passage, and means biassing the closure member towards its open position, wherein the larger diameter region is sealingly and slidably engaged with a wall of the recess.

By arranging the larger diameter region of the closure member to engage with the wall of the recess rather than within the hollow of a plug in the recess, it is possible to use a materially larger diameter for a given size of valve body. This in turn permits the smaller diameter region of the closure member, and thereby the sealing surface around the flow passage, to be made materially larger, with the result that the flow restriction in this region of the flow passage can be materially reduced.

Preferably, the recess in which the closure member is provided is axially aligned with the outlet connection.

Preferably also, the recess in which the closure member is provided (i) extends transversely with respect to a control recess in which the closure member is provided, and (ii) is displaced from the control recess but communicates therewith via the intermediate passage region.

Additionally or alternatively, in a second aspect of the present invention, flow restriction can be reduced in a flow control valve assembly of the type having a pressure retaining device with smaller and larger diameter regions if the above-described angled drilling defining an intermediate region of the flow passage between the inlet and outlet connections is replaced by an intermediate passage region formed by a milling or other machining operation, and is preferably an electrochemical machining operation. Such milling or other machining operation permits a larger hole (with consequential lower flow restriction) to be provided than is conveniently possible with an angled drilling which usually takes place through the outlet connection.

In a preferred arrangement, the valve body has a control recess therein in which the moveable valve member and the valve seat are located, the control recess is spaced from and extending transversely with respect to the outlet connection and the recess accommodating the closure member, and the machined passage region extends transversely from the control recess to a location adjacent to the sealing surface.

The intermediate passage region may be formed by a milling operation performed from within the control recess. However, it is preferred to form the intermediate passage region by an electrochemical machining operation. Such electrochemical machining operation is preferably effected using an electrode disposed within the control recess, and is more preferably augmented by a further electrode disposed within the recess accommodating the closure member.

We have found that it is possible to use the same design of pressure retaining device with either of the above-described standard types of outlet connector ( ie internally threaded or externally threaded). Thus, it is possible to provide a common design of valve body which can then be subsequently finished, e.g. by machining, at the appropriate locations in order to form the desired outlet connection of either conventional type. Thus, a common basic design of valve body and valve internal parts including the pressure retaining device can be used irrespective of the type of standard outlet connection required.

Thus, according to a third aspect of the present invention, there is provided, in a method of manufacturing flow control valve assemblies, the steps of (a) forming a plurality of identical unitary valve bodies, each body having a first body region destined to be shaped to define (i) an inlet connection and (ii) a control recess in which a moveable valve member is to be assembled, and a second body region extending transversely relative to the first body region, the second body region being destined to be shaped to define (i) an outlet connection and (ii) a recess for receiving a pressure retaining device; (b) on the second body regions of some of said valve bodies, providing an externally screwthreaded outlet connection; and (c) on the second body regions of others of said valve bodies providing an internally screw-threaded outlet connection.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a sectional view of a flow control valve assembly according to one example of the present invention, Fig 2 is a sectional view of the valve body illustrated in Fig. 1 showing how part of a flow passage therein is formed, Fig 3 is a sectional view taken at right angles to the section shown in Fig 2, Fig 4 is a section similar to Fig 3 but showing the installation of a pressure retaining device in the valve body, Fig 5 is a section similar to Fig 4 but with an externally screw-threaded outlet connection, and Figs. 6 and 7 are sectional views showing the positioning of electrodes for performing electrochemical machining and de-burring operations within the valve body.

Referring now to Figs 1 to 4 of the drawings, the flow control valve assembly is for attachment to a gas cylinder (not shown), and includes a brass valve body 10 formed, in this embodiment, by stamping and subsequent machining operations. In its as-stamped form, the valve body 10 comprises first and second body regions 10a and 10b which extend mutually transversely. As viewed in Figs 1 and 2, the first body region 10a is machined subsequent to stamping of the body 10 so as to produce an externally screw-threaded, tapering inlet connection 12 which is of a standard size for screwing into a standard, internally screw-threaded hole at one end of the gas cylinder. The body region 10a is also machined with a stepped control recess 14 which includes an annular valve seat 16 communicating with the inlet connection 12 via a first flow passage region 18.The control recess 14 has a conventional moveable valve member 20 mounted therein and axially moveable towards and away from the valve seat 16 by means of a stem 22 which can be manually rotated by means of a hand wheel 24 in a manner known per se. A gland seal and packing assembly 26 are provided for sealing the opening to the control recess 14 around the stem 22. In the condition illustrated in Fig 1, the valve member 20 is closed down on to the valve seat 15 so as to prevent flow of gas from the first flow passage region 18 into the recess 14.

In this embodiment, the first flow passage 18 is defined by (i) a blind bore 18a extending downwardly from the control recess 14 on the opposite side of the valve seat 16, and (ii) a drilling 18b extending upwardly through the inlet connection 12 parallel to the bore 18a and overlapping therewith at region 18c. The region 18c is electrochemically de-burred as will be described hereinafter with reference to Figs 6 and 7.

In an alternative embodiment (as disclosed in British Patent Application No. 9417168.3 from which the present Application claims priority and whose disclosure is incorporated herein by reference), the first flow passage 18 may be formed by oppositely directed relatively short bores extending respectively downwardly from the valve seat 16 and upwardly from the inlet connection 12, and an inclined drilling interconnecting such bores.

The second body region 10b (see particularly Fig 3) is machined from both ends so as to define an outlet connection 28 at one end and a recess 30 at the other end. The outlet connection 28 and the recess 30 are mutually coaxial and extend perpendicularly with respect to the control recess 14 but transversely displaced therefrom. The outlet connection 28 in the embodiment illustrated in Figs 1 to 4 is internally screw threaded over region 28a. However, an identical as-stamped valve body 10 may be machined so as to produce the type of outlet connection 28 as illustrated in Fig 5 which is externally screw threaded at 28b and which is machined slightly differently internally so as to satisfv the standard for such an externally screw threaded outlet connection.Apart from this, the valve body of Fig 5 is produced in exactly the same way as that illustrated in Figs 1 to 4 and is fitted with exactly the same components to be described hereinafter. The machining operation performed internally of the body region 10b in both cases is such as to cause the recess 30 to communicate with an intermediate region of the flow passage leading from the inlet connection 12 to the outlet connection 28 via an annular sealing surface 32.

The annular sealing surface 32 has a diameter which is only slightly less than that of the adjacent region of the recess 30. The outer end region of the recess 30, i.e. that region which is remote from the annular sealing surface 32, is internally screw threaded at 30a.

The control recess 14 communicates with the end of the recess 30 adjacent to the annular sealing surface 32 by means of a slot 34 defining part of the intermediate region of the flow passage. In this embodiment, the slot 34 is formed by an electrochemical machining operation as described hereinafter with reference to Figs. 6 and 7. The slot 34 thereby produced has a considerable dimension in the axial direction of the recess 30 as well as in a direction perpendicular thereto. As can be seen from Fig 3, the right hand end of the slot 34 opens into the recess 30 adjacent a frusto-conically inwardly tapering shoulder 38.

In an alternative embodiment (as disclosed in the above-mentioned British Patent Application No. 9417168.3 from which priority is claimed), the slot 34 is formed by a milling operation using a milling cutter which is introduced via the control recess 14.

Disposed within the recess 30 is a pressure retaining device indicated generally by arrow 40 (see Fig 4). The pressure retaining device 40 comprises a closure member 42 which is stepped inwardly at its end adjacent the annular sealing surface 32 so as to provide axially spaced smaller and larger diameter regions 44 and 46, respectively which are fitted with o-ring seals. The closure member 42 is urged into a closed position as illustrated in Fig 4 by means of a compression spring 47 which extends between the closure member 42 and a hollow closure plug 48 which is externally screw threaded and which engages with the internal threading 30a in the recess 30. In its closed position as illustrated in Fig 4, the o-ring seal on the smaller diameter region 44 sealingly engages with the annular sealing surface 32 so as to prevent communication between the slot 34 and the outlet connection 28.In this condition, the o-ring seal on the larger diameter region 46 of the closure member 42 is sealingly engaged with the peripheral wall of the recess 30 with the slot 34 being disposed between the o-ring seals.

The closure member 42 is hollow and is provided with a small vent hole 50 at its forward end and a recess 52 at its rear end for receiving the adjacent end of the spring 47. In an alternative embodiment (as disclosed in British Patent Application No. 9417168.3 form which priority is claimed), the recess 52 is replaced by a sleeve extending from the rear end of the closure member 42 and serving as a guide for the spring 47 and also as a stop.

In normal use, when it is desired to supply gas under pressure from a cylinder attached to the inlet connection 12 to a system which is connected to the outlet connection 28, the hand wheel 24 is rotated so as to move the valve member 20 away from its seat 16. This permits gas under pressure to pass along the passage region 18, into the control recess 14, and into the slot 34 which defines part of the intermediate region of the flow passage. Thus, pressure is exerted on the closure member 42. Although the step on the closure member 42 between the smaller and larger diameter regions 44 and 46 abuts against the frustoconical shoulder 38, sealing does not take place here but takes place between the o-ring seal on the region 46 and the annular sealing surface 32. Thus, a net pressure differential is exerted on the closure member 42 in a direction such as to urge the latter away from its closed position against the action of spring 47 and into an open position in which flow of gas under pressure is permitted through the slot 34 past the annular sealing surface 32 and into the outlet connection 28 so as to be supplied to the system. It will be appreciated that such movement of the closure member 42 is permitted without there being a build-up of pressure in the recess 30 behind the closure member 42 because of the provision of the vent hole 50.

When the hand wheel 24 is rotated to close the valve member 20 down onto the seat 16, or when the gas pressure within the cylinder reaches a predetermined low level, it will be understood that the pressure at the slot 34 will drop to a level such that it is no longer capable of overcoming the action of the spring 47 which then moves the closure member 42 back into the closed position as illustrated in Fig. 4 so as to prevent unwanted risk of material or dirt leaking back along the system and into the gas cylinder.

When it is desired to re-fill the gas cylinder, a specially adapted re-filling nozzle is engaged with the outlet connection 28. Such nozzle (not shown) has a special nose which bears against the exposed end of the closure member 42 so as to urge it out of its closed position against the action of the spring 47 until the slot 34 is completely exposed. This permits re-filling of the gas cylinder to take place without undue flow restriction because the diameter of the annular sealing surface 32 has been maximised, as have the dimensions of the slot 34. Undue compression of the spring 47 is prevented when re-filling because of engagement of the rear end of the closure member 42 against the adjacent internal end surface of the plug 48.

Unauthorised re-filling of the cylinder without using the specially adapted re-filling nozzle with nose which bears against the closure member 42 is not possible. Simply applying gas pressure to the outlet connector 28 will not move the closure member 42 because the provision of the vent hole 50 causes such gas pressure also to be transmitted to the opposite end of the closure member 42 to augment the action of the spring 47.

To effect the previously mentioned electrochemical machining and deburring operations within the valve body 10, a first electrode 60 is introduced into the control recess 14 so that (i) a shaped nose 60a of the electrode extends through the valve seat 16 and into the blind bore 18a and (ii) a larger diameter region 60b of the electrode 60 lies opposite the region where the slot 34 is to be electrochemically machined (Fig.6). As shown in Fig. 7, a second electrode 62 is introduced into the recess 30 so that a part 62a of the electrode 62 lies opposite the region where the slot 34 is to be formed. Electrochemical machining of the slot 34 and de-burring of the region 18c is then effected by passing an electrolyte through the control recess 14 and passage 18 and through the recess 30 and the outlet connection 28, whilst passing a current between each electrode 60, 62 and the valve body 10. The electrochemical procedure involving electrode 60 also serves to de-burr a hole 64 (shown in Fig. 6 only) providing communication between the upper end of the drilling 18b and the exterior of the valve body 10 and accommodating a bursting disc (not shown) arranged to burst if the internal pressure exceeds a predetermined safe maximum value.

Claims (10)

1. A flow control valve assembly for attachment to a gas cylinder, said assembly comprising a valve body having an inlet connector adapted to be attached to a gas cylinder and an outlet connector adapted to be attached to a system to be pressurised with gas from the cylinder in use; a flow passage in the valve body providing communication between the inlet and the outlet connectors; a valve seat in the flow passage; a moveable valve member mounted in the body for movement towards and away from the valve seat in order to control the flow of gas in the flow passage in use; and a pressure retaining device mounted in the valve body and arranged to close the flow passage in use when the pressure in the flow passage falls below a predetermined value, the pressure retaining device including a closure member disposed in a recess in the valve body, the recess opening into an intermediate region of the flow passage leading to the outlet connection, the closure member having mutually spaced, smaller and larger diameter regions and being moveable between a closed position in which the smaller diameter region engages a sealing surface which extends around the flow passage and an open position in which the smaller diameter region is disposed within the recess and out of the flow passage, and means biassing the closure member towards its open position, wherein the larger diameter region is sealingly and slidably engaged with a wall of the recess.

2. A flow control valve assembly as claimed in claim 1, wherein the recess in which the closure member is provided is axially aligned with the outlet connection.

3. A flow control valve assembly as claimed in claim 1 or 2, wherein the recess in which the closure member is provided (i) extends transversely with respect to a control recess in which the closure member is provided, and (ii) is displaced from the control recess but communicates therewith via the intermediate passage region.

4. A flow control valve assembly for attachment to a gas cylinder, said assembly comprising a valve body having an inlet connector adapted to be attached to a gas cylinder and an outlet connector adapted to be attached to a system to be pressurised with gas from the cylinder in use; a flow passage in the valve body providing communication between the inlet and the outlet connectors; a valve seat in the flow passage; a moveable valve member mounted in the body for movement towards and away from the valve seat in order to control the flow of gas in the flow passage in use; and a pressure retaining device mounted in the valve body and arranged to close the flow passage in use when the pressure in the flow passage falls below a predetermined value, the pressure retaining device including a closure member disposed in a recess in the valve body, the recess opening into an intermediate region of the flow passage leading to the outlet connection, the closure member having mutually spaced, smaller and larger diameter regions and being moveable between a closed position in which the smaller diameter region engages a sealing surface which extends around the flow passage and an open position in which the smaller diameter region is disposed within the recess and out of the flow passage, and means biassing the closure member towards its open opposition, wherein the intermediate region of the flow passage is formed by a milling or other machining operation.

5. A flow control valve assembly as claimed in claim 4, wherein the intermediate passage region is formed by an electrochemical machining operation.

6. A flow control valve assembly as claimed in claim 4 or 5, wherein the valve body has a control recess therein in which the moveable valve member and the valve seat are located, the control recess is spaced from and extending transversely with respect to the outlet connection and the recess accommodating the closure member, and the machined passage region extends transversely from the control recess to a location adjacent to the sealing surface.

7. A flow control valve assembly having the combination of features as claimed in any one of claims 1 to 3 and any one of claims 4 to 6.

8. A flow control valve assembly as claimed in claim 1 and/or claim 4, substantially as hereinbefore described with reference to the accompanying drawings.

9. In a method of manufacturing flow control valve assemblies, the steps of (a) forming a plurality of identical unitary valve bodies, each body having a first body region destined to be shaped to define (i) an inlet connection and (ii) a control recess in which a moveable valve member is to be assembled, and a second body region extending transversely relative to the first body region, the second body region being destined to be shaped to define (i) an outlet connection and (ii) a recess for receiving a pressure retaining device; (b) on the second body regions of some of said valve bodies, providing an externally screw threaded outlet connection; and (c) on the second body regions of others of said valve bodies, providing an internally screw-threaded outlet connection.

10. A method as claimed in claim 9, substantially as hereinbefore described with reference to the accompanying drawings.

10. A method as claimed in claim 9, substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A flow control valve assembly for attachment to a gas cylinder, said assembly comprising a valve body having an inlet connector adapted to be attached to a gas cylinder and an outlet connector adapted to be attached to a system to be pressurised with gas from the cylinder in use; a flow passage in the valve body providing communication between the inlet and the outlet connectors; a valve seat in the flow passage; a moveable valve member mounted in the body for movement towards and away from the valve seat in order to control the flow of gas in the flow passage in use; and a pressure retaining device mounted in the valve body and arranged to close the flow passage in use when the pressure in the flow passage falls below a predetermined value, the pressure retaining device including a closure member disposed in a recess in the valve body, the recess opening into an intermediate region of the flow passage leading to the outlet connection, the closure member having mutually spaced, smaller and larger diameter regions and being moveable between a closed position in which the smaller diameter region engages a sealing surface which extends around the flow passage and an open position in which the smaller diameter region is disposed within the recess and out of the flow passage, and means biassing the closure member towards its closed position, wherein the larger diameter region is sealingly and slidably engaged with a wall of the recess.

2. A flow control valve assembly as claimed in claim 1, wherein the recess in which the closure member is provided is axially aligned with the outlet connection.

3. A flow control valve assembly as claimed in claim 1 or 2, wherein the recess in which the closure member is provided (i) extends transversely with respect to a control recess in which the closure member is provided, and (ii) is displaced from the control recess but communicates therewith via the intermediate passage region.

4. A flow control valve assembly for attachment to a gas cylinder, said assembly comprising a valve body having an inlet connector adapted to be attached to a gas cylinder and an outlet connector adapted to be attached to a system to be pressurised with gas from the cylinder in use; a flow passage in the valve body providing communication between the inlet and the outlet connectors; a valve seat in the flow passage; a moveable valve member mounted in the body for movement towards and away from the valve seat in order to control the flow of gas in the flow passage in use; and a pressure retaining device mounted in the valve body and arranged to close the flow passage in use when the pressure in the flow passage falls below a predetermined value, the pressure retaining device including a closure member disposed in a recess in the valve body, the recess opening into an intermediate region of the flow passage leading to the outlet connection, the closure member having mutually spaced, smaller and larger diameter regions and being moveable between a closed position in which the smaller diameter region engages a sealing surface which extends around the flow passage and an open position in which the smaller diameter region is disposed within the recess and out of the flow passage, and means biassing the closure member towards its closed position, wherein the intermediate region of the flow passage is formed by a milling or other machining operation.

5. A flow control valve assembly as claimed in claim 4, wherein the intermediate passage region is formed by an electrochemical machining operation.

6. A flow control valve assembly as claimed in claim 4 or 5, wherein the valve body has a control recess therein in which the moveable valve member and the valve seat are located, the control recess is spaced from and extending transversely with respect to the outlet connection and the recess accommodating the closure member, and the machined passage region extends transversely from the control recess to a location adjacent to the sealing surface.

7. A flow control valve assembly having the combination of features as claimed in any one of claims 1 to 3 and any one of claims 4 to 6.

8. A flow control valve assembly as claimed in claim 1 and/or claim 4, substantially as hereinbefore described with reference to the accompanying drawings.

9. In a method of manufacturing flow control valve assemblies, the steps of (a) forming a plurality of identical unitary valve bodies, each body having a first body region destined to be shaped to define (i) an inlet connection and (ii) a control recess in which a moveable valve member is to be assembled, and a second body region extending transversely relative to the first body region, the second body region being destined to be shaped to define (i) an outlet connection and (ii) a recess for receiving a pressure retaining device; (b) on the second body regions of some of said valve bodies, providing an externally screw threaded outlet connection; and (c) on the second body regions of others of said valve bodies, providing an internally screw-threaded outlet connection.