GB2284449A

GB2284449A - Pump valve arrangement

Info

Publication number: GB2284449A
Application number: GB9323307A
Authority: GB
Inventors: Trevor Hicks; Lawrence Bottomley
Original assignee: ENGLAND WORTHSIDE Ltd
Current assignee: ENGLAND WORTHSIDE Ltd
Priority date: 1993-11-11
Filing date: 1993-11-11
Publication date: 1995-06-07
Also published as: GB9323307D0

Abstract

In a pump a first one way valve 18 is mounted on a piston 13 to permit fluid flow past the piston, and a second one way valve 19 permits fluid to flow through an inlet port 6. Each valve 18, 19 comprises a valve member 21 supported by a carrier member 20 which defines a valve seat for the respective valve member. The two carrier members 20 are substantially identical to each other and the two valve members 21 are substantially identical to each other. A casing 35 is provided outside cylinder body 1 to provide a coolant space therebetween. <IMAGE>

Description

A PUMP The present invention relates to a pump and in particular to a piston pump for lifting fluid.

Piston pumps of various forms have been in use for many years in a wide variety of applications. A known pump used for pumping beer from a cask to a dispensing point is illustrated in Fig. 1 (which is an exploded illustration). The pump, which is fitted into a beer supply line between a source (typically a cask) and a dispensing point (typically a hand pulled dispenser at a bar), comprises a cylinder (a) closed at both ends by respective end caps (b) and (c). The cylinder (a) has an outlet (d) defined by end cap (b) and an inlet (e) defined by end cap (c).

A piston (f) is slidably disposed within the cylinder (a) for reciprocating motion between the outlet (d) and the inlet (e).

Movement of the piston (f) is effected by a piston rod (g) which extends through the end cap (b) and is connected to a hand operated lever (not shown) at the dispensing point.

A first spring loaded poppet valve (h) is carried by the piston (f) and a second spring loaded poppet valve (i) is housed in the end cap (c) within the inlet (e). The basic arrangement is very well known; the pump operates, by movement of the piston (f) and operation of the valves (h) and (i), to pass fluid through the cylinder (a) in one direction only, i.e. from the inlet (e) to the outlet (f). Each stroke of the pump delivers a measured volume of beer equal to the volume of the cylinder (a) downstream of the piston (f) when the piston is at the inlet end of the cylinder (a).

The pump described above has several disadvantageous features.

Firstly, each of the valves (h) and (i) has a valve seat defined by an element (fl) of the piston (f) and by the end cap (c) respectively. To ensure that the valves do not leak, each valve seat must be very accurately formed. Thus both the element (fl) and the end cap (c) are relatively expensive to produce as they must be manufactured by a consistently accurate method, such as a precise moulding process.

Secondly, it is periodically necessary for the pump to be dismantled for maintenance purposes. This can cause problems as the pump incorporates a number of seals (j) which must be assembled accurately if the pump is to be leak free and work correctly. It is often the case that such repairs are performed by semi-skilled labour in which case it is likely that one or more of the seals (j) will not be reassembled correctly and that subsequent operation of the pump will be adversely affected.

Thirdly, the operator of the pump (e.g., the publican) is required to periodically sterilise the pump and fluid circuit by a chemical cleaning process. Every additional joint and/or seal creates stagnant regions that considerably increase the degree of difficulty in ensuring complete cleanliness. Unless meticulous methods and application are applied, it is also possible to contaminate the drink with chemical cleaner in the event that it is not completely flushed clear of the pump. As it is often the case that poor standards and inadequate methods are employed, this can be a significant problem.

Fourthly, joints andlor seals create biological breeding grounds, especially with beer and similar drinks that contain live organisms such as yeast. The relatively large number of seals used in existing pumps of the type described above is therefore undesirable.

It is an object of the present invention to provide a pump which obviates or mitigates the above problems.

According to a first aspect of the present invention there is provided a pump, comprising a cylinder having an inlet port and an outlet port, a piston arranged for reciprocal motion within the cylinder between the inlet port and the outlet port, a first one way valve mounted on the piston to permit fluid flow past the piston in one direction only, ar.d a second one way valve which permits fluid to flow through the inlet port ito the cylinder, the arrangement of the valves being such that fluid flow through the cylinder is permitted from the inlet port to the outlet port only, wherein each valve comprises a valve member supported by a carrier member, each carrier member defines a valve seat for the respective valve member, the two carrier members are substantially identical to each other, and the two valve members are substantially identical to each other.

Thus with the present invention, in which the two carrier members which define the valve seats and the valve members are substantially identical, the number of components which must be made to a high degree of accuracy is reduced as compared with the prior art. This reduces the cost of manufacture of the pump.

Preferably the cylinder and/or the piston and/or the valve members and/or the carrier members is! are formed from moulded plastics material.

Preferably the first valve means is releasably mounted on the piston. This, for example, allows the valve means to be dismantled from the piston for cleaning and maintenance operations. The carrier member may, for instance, be in screw-threaded engagement with the piston.

Preferably the cylinder comprises a generally cup shaped body portion and an end cap which defines the inlet port, and said second valve means is mounted, preferably releasably, in said end cap. The carrier member of the second valve means may, for instance, be in screw-threaded engagement with the end cap.

A sealing member, such as an elastomeric O-ring, is preferably disposed between the body portion and the end cap to provide a fluid tight seal between the two.

Preferably the valve means are formed such that each valve member can be supported by the respective carrier member in either a first orientation so as to permit fluid to flow in one direction relative to the carrier, or a second orientation so as to permit fluid to flow in the opposite direction relative to the carrier.

Preferably each carrier member is generally cylindrical and has an internal surface which tapers inwardly from each axial end of the carrier member so as to define a first generally conical surface at one axial end of the carrier member and a second generally conical surface at the other axial end of the carrier member, the first conical surface providing a valve seat for the valve member when in the first orientation and the second conical surface providing a valve seat for the valve member when in the second orientation.

The valve members may be of any suitable type and are preferably poppet valves, each defining a respective valve head and valve stem.

Preferably each valve member supports a sealing member which is disposed between the respective valve member and valve seat when the valve is closed.

Preferably each valve means includes a valve spring which tends to hold the respective valve member in the closed position, each valve spring being helical and disposed around the respective valve stem in a state of compression between a central portion of the respective carrier member and an abutment provided on the valve stem.

The said abutment may, for instance, be a star washer pushed onto the end of the respective valve stem.

Preferably the piston is a moulded member and is moulded onto the end of a piston rod which extends from the cylinder and which is used to effect movement of the piston within the cylinder.

According to a second aspect of the present invention there is provided a valve member supported by a carrier member, the carrier member defining a valve seat for the valve member, wherein the valve member can be supported by the carrier member in either a first orientation so as to permit fluid to flow in one direction relative to the carrier member, or a second orientation so as to permit fluid to flow in the opposite direction relative to the carrier member.

Preferably the carrier member is generally cylindrical and has an internal surface which tapers inwardly from each axial end of the carrier member so as to define a first generally conical surface at one end of the axial member and a second generally conical surface at the other end of the carrier member, the first conical surface providing a valve seat for the valve member when in the first orientation and the second conical surface providing a valve seat for the valve member when in the second orientation.

According to a third aspect of the present invention, there is provided a pump, comprising a cylinder through which pumped fluid flows, the cylinder having two axially spaced apart radially outwardly extending annular flanges. at least one of said flanges being moveable relative to the cylinder so as to vary the axial separation of the flanges, an outer cylindrical casing disposed around the cylinder between the two flanges so as to define an annular chamber around the cylinder to receive cooling fluid, and compression seals disposed between the two flanges and respective axial ends of the outer casing.

Thus by appropriate positioning of the or each moveable flange relative to the cylinder, the seals can be put under a desired amount of compression sufficient to provide a good fluid tight seal.

Preferably the or each moveable flange can be mounted on the cylinder in a predetermined position such that the compression seals are compressed to a desired amount to provide a fluid tight seal between the outer casing and the flanges.

By predetermining the position of the or each moveable flange it can be readily ensured that the seals are always compressed by the desired amount.

The cylinder may be provided with an abutment which limits the axial movement of the or each moveable flange so that when the or each moveable flange abuts against the or each abutment the flanges are at a minimum axial separation and the compression seals are compressed by a desired amount to provide a good fluid tight seal between the outer casing and the flanges.

Preferably the outer casing is held in position relative to the cylinder by the flanges.

Preferably each flange is provided with an annular groove to receive a respective compression seal and a respective axial end of the outer casing.

Preferably the or each moveable flange is in screw-threaded engagement with the cylinder.

According to a fourth aspect of the present invention there is provided a pump, comprising a cylinder having an inlet port and an outlet port, wherein the cylinder comprises a generally cup shaped body portion and an end cap.

Preferably an annular compression seal is disposed between the end cap and the cylinder body portion.

Preferably the end cap can be mounted on the cylinder body portion in a predetermined position in which the compression seal is compressed to a desired amount to provide a good fluid tight seal.

Preferably the end cap can be mounted on the cylinder body portion in a predetermined position in which the compression seal is compressed by a desired amount to provide a good fluid tight seal.

Preferably the end cap is in screw-threaded engagement with the cylinder body portion, and the cylinder body portion is provided with an abutment whereby screwing the end cap up to the abutment puts the compression seal under a desired amount of compression to provide a good fluid tight seal between the end cap and the cylinder body portion.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of the exploded prior art pump described above; Fig. 2 is a cross-section of a pump in accordance with the present invention; and, Figs. 3a to 8b show various components of the pump of Fig. 2.

Referring to the drawings, and in particular to Fig. 2, the illustrated pump according to the present invention comprises a generally cup-shaped cylinder body 1 closed at one end by a removable end cap 2 which is screwed onto the respective end of the body 1. An elastomeric O-ring 3 is compressed between the end of the cylinder body 1 and the end cap 2 to provide a good fluid tight seal between the two. The O-ring 3 seats within an annular abutment shoulder 41 defined by the axial end of a cylinder body 1. The arrangement is such that by screwing the end cap 2 onto the cylinder body 1 into abutment with the abutment shoulder 4i, the O-ring 3 is compressed by a predetermined desired amount.

Both the cylinder body I and the end cap 2 are moulded plastics components and are shown in isolation from other components of the pump in Figs. 3a to 4b. Fig. 3a is an axial section of the cylinder body 1 and Fig. 3b is an end view of the cylinder body 1 looking in the direction of arrow A of Fig. 3a. Fig. a is an axial section of the end cap 2 and Fig. 4b is an end view of the end cap 2 looking in the direction of arrow B of Fig. 4a.

The end cap 2 is formed with an internal cavity 4 and an integral axially extending nozGie 5 which defines an inlet port 6 which opens into the cavity 4. The cavity 4 houses valve means as described in detail below. From Fig. a it will be seen that the external surface of the end cap 2 is provided with a central raised hexagonally shaped portion 7 which is provided to receive a spanner (not shown) to enable the end cap 2 to be screwed firmly onto the end of the cylinder body 1.

The end of the cylinder body 1 opposite the end cap 2 defines an outlet port 8 and an axially outwardly projecting hollow cylindrical boss 9 which provides a guide bore 10 for an elongate piston rod 11 which extends into the interior of the cylinder body 1.

Referring again to Fig. 2, the end of the piston rod 11 is moulded into a boss 12 defined by a moulded plastics piston 13. The piston 13 is shown in isolation from other components of the pump in Figs. 5a and 5b; Fig. Sa being an axial cross section of the piston 13 and Fig. 5b being an end view looking in the direction of arrow C of Fig. 5a. The piston 13 is generally cylindrical and is in slidable contact with the inner wall of the cylinder body 1. An annular groove 14 is formed in the outer surface of the piston 13 and receives an Oring 15 and annular sealing member 16 by means of which a fluid tight seal is formed between the piston 13 and the wall of the cylinder body 1.

The piston 13 is hollow, defining a central cavity 17, and is open at both axial ends. The boss 12 which receives the piston rod 11 is joined to the cylindrical wall of the piston 13 by three equispaced radial arms 18 (shown in Fig. 5b).

The cavity 17 defined by the piston 1 and the cavity 4 defined by the end cap 2 are both adapted to receive substantially identical valve means 18 and 19 which are described below and are shown in isolation from other components of the pump in Fig. 6a and Fig. 6b respectively.

Each valve means 18 and comprises a moulded plastics carrier member 20 which supports a spring loaded poppet valve 21. The two carrier members 20 are identical and so only one will be described in detail. A valve carrier member 20 is illustrated in isolation from other components of the pump in Pigs. 7a and 7b; Fig. 7a is an axial section of the member 20 and Fig. 7b is an end view looking in the direction of arrow D of Fig. 7a.

Each valve carrier member 20 is hollow and generally cylindrical.

The internal diameter of the carrier member 20 decreases from each end towards the it's axial centre. A circular central support portion 22 is positioned midway between the axial ends of the carrier member 20 and is connected to it's inner wall by three equispaced radial support arms 23. The configuration of the carrier member 20 is such that the openings defined in it's axial ends are conical, tapering inwardly towards the axial centre of the member 20, and define valve seats 24 and 25 respectively.

The carrier member 20 is provided with an external annular 26 flange in between it's axial ends. One end 27 of the carrier member 20 on one side of the flange 26 is externally screw threaded. The opposite face of the flange 26 is provided with four circumferentially equispaced blind bores 28.

The screw threaded end 27 enables the carrier member 20 to be screwed into either the cavity 17 in the piston 13 or the cavity 4 in the end cap 2; the blind bores 28 enable the carrier member 20 to be tightened in position by use of a suitable tool (not shown).

Referring to Figs. 6a and 6b, each poppet valve 21 (one of which is shown in detail in Figs. 8a and 8b, Fig. 8b being an end view looking in the direction of arrow E of Fig. 8a) is supported by a respective carrier member 20 with the valve stem 29 passing through the central support portion 22. A coil spring 30 is disposed around the valve stem 29 between the support portion 22 and a star washer 31 which is pushed onto the end of the valve stem 29. The coil spring 30 acts to hold the valve 21 in a closed position in the absence of sufficient fluid pressure to open it.

The valve means 18 and 19 differ only in that the poppet valves 21 are supported by the carrier members 20 so as to extend in opposite axial directions relative to the respective carrier members 20.

The carrier members 20 are configured so that whichever way the respective poppet valve 21 is supported by the carrier 20 one of the conical surfaces 24 or 25 will provide a valve seat. For valve means 18 surface 24 provides the valve seat and for valve means 19 surface 25 provides the valve seat. Thus, referring to Fig. 2, although the two carrier members 20 lie in opposite axial directions, the poppet valves 21 are arranged so as to function as required.

Each poppet valve head 32 supports an elastomeric O-ring 33 in an annular groove 34 defined by the respective valve head 33 to provide a fluid tight seal between the valve and the valve seat when the valve is closed.

The cylinder body 1 is provided with an insulating outer cylindrical casing 35. The insulating casing 35 is fitted between an annular flange 36 of the end cap 2 and an annular flange 37 of the cylinder body 1, the axial ends of the casing 35 being received within annular grooves 39 and 40 defined by respective flanges 37 and 36.

Sealing O-rings 38 are disposed within the grooves 39 and 40 between the ends of the casing 35 and respective flanges 36 and 37 to provide a fluid tight seal. Water is then pumped through the annular space defined between the casing 35 and the outer wall of the cylinder body 1 to keep the contents of the cylinder cool. The axial length of the casing 35, the depth of the grooves 39 and 40 and the thickness of the O-rings 38, are all selected so that when the end cap 2 is screwed up to the abutment shoulder 41 the O-rings 38 are compressed to a desired predetermined amount.

In use, inlet nozzle 5 is connected to a fluid source (not shown), e.g. to a line from a beer cask, and the outlet port 8 is connected to a dispensing pipe (not shown), e.g. at a bar. The pump is operated by movement of the piston 13 via the piston rod 11 (which is for instance connected to a lever at a bar) and functions in essentially the same manner as the prior art pump discussed above to pass fluid, e.g. beer, through the cylinder from the inlet 6 to the outlet 8.

The maximum volume of fluid that can be dispensed by the pump in a single stroke is equivalent to the volume of the cylinder body 1 behind the piston 13 when the piston 13is pushed to the inlet end of the cylinder body 1. The pump can be dimensioned to give any desired maximum. For applications as a beer pump, the pump will typically be dimensioned to deliver fluid in 1/4 or 1/3 pin volumes.

From the above it will be evident that the pump in accordance with the present invention is constructed to overcome the problems discussed in the introduction to this specification in relation to the prior art. In particular the valves 21 are carried by identical valve carrier members 20 which define the valve seats. Thus only one accurate moulding is required instead of two as in the case of the prior art pump of Fig. 1.

By locating the valve seals 33 on the valve heads 32 as oppose to the valve seats the mounting direction of each valve 21 relative to the axial direction of the respective carrier 20 is reversible without unduly complicating the structure of the carrier 20.

In addition, the pump described above in accordance with the present invention incorporates relatively few seals and/or joints as compared with prior art pumps and thus the problems associated with seals and/or joints discussed in the introduction to the specification are greatly reduced.

It will be appreciated that the detailed structure of the pump, e.g. the structure of the cylinder, the end cap 2 and the piston 13, can be varied considerably whilst still retaining the benefit offered by the present invention in providing identical valve carriers for the two valves.

In the embodiment of the invention described above the structure of the cylinder is advantageous in that it is formed from only two parts, i.e. the cylinder body 1 and the end cap 2, and thus only a single seal 3 is required as oppose to two seals as in the three part cylinder of the prior art pump of Fig. 1. This simplifies reassembly of the pump after cleaning or maintenance operations.

In addition, since the boss 9 which guides and supports the piston rod 11 is moulded integrally with the cylinder body 1 the number of seals required is further reduced relative to the prior art pump of Fig. 1.

With the valves 21 and valve carriers 20 described above, the direction of the valve is reversible relative to the axial direction of the carrier member. However this need not necessarily be the case.

For instance, referring to the carrier 20 described above, the external surface of the carrier 20 could be screw-threaded on both sides of the flange 26 so that the carrier can be screwed into the piston 13 or the end cap 2 while facing in the same axial direction in the finished pump. In this case one of the valve seats 24 or 25 could be dispensed with. It will be appreciated that even with such a modified embodiment of the present invention the carrier members can still be identical to each other.

It will be appreciated that in the above described, or any other, embodiment of the invention, the cylinder need not have a circular cross-section. For instance, the cylinder and piston could have complementary oval or polygonal cross sections.

It will also be appreciated that the present invention could be embodied in a pump having more than two valve means and/or having valve means other than poppet valves, e.g. flap valves.

Claims

1. A pump, comprising a cylinder having an inlet port and an outlet port, a piston arranged for reciprocal motion within the cylinder between the inlet port and the outlet port, a first one way valve mounted on the piston to permit fluid flow past the piston in one direction only, and a second one way valve which permits fluid to flow through the inlet port into the cylinder, the arrangement of the valves being such that fluid flow through the cylinder is permitted from the inlet port to the outlet port only, wherein each valve comprises a valve member supported by a carrier member, each carrier member defines a valve seat for the respective valve member, the two carrier members are substantially identical to each other, and the two valve members are substantially identical to each other.

2. A pump according to claim 1, wherein the carrier member of the first valve is releasably mounted on the piston

3. A pump according to claim 2, wherein the carrier member of the first valve is in screw-threaded engagement with the piston.

4. A pump according to any preceding claim, wherein the cylinder comprises a generally cup shaped body portion and an end cap, and the second valve is mounted in the end cap.

5. A pump according to claim 4, wherein the end cap and body portion are separable, and a sealing member is disposed between the body portion and the end cap to provide a fluid tight seal between the two.

6. A pump according to any one of claims 4 or 5, wherein the end cap defines the inlet port and the second valve is mounted in the end cap within inlet port.

7. A pump according to any one of claims 4 to 6, wherein the second valve is releasably mounted in the end cap.

8. A pump according to claim 7, wherein the carrier member cf the second valve is in screw-threaded engagement with the end cap.

9. A pump according to any preceding claim, wherein the valves are formed such that each valve member can be supported by the respective carrier member in either a first orientation so as to permit fluid to flow in one direction relative to the carrier, or a second orientation so as to permit fluid to flow in the opposite direction relative to the carrier.

10. A pump according to claim 9, wherein each carrier member is generally cylindrical and has an internal surface which tapers inwardly from each axial end of the carrier member so as to define a first generally conical surface at one axial end of the carrier member and a second generally conical surface at the other axial end of the carrier member, the first conical surface providing a valve seat for the valve member when in the first orientation and the second conical surface providing a valve seat for the valve member when in the second orientation.

11. A pump according to any preceding claim. wherein the valve members are poppet valves, each defining a respective valve head and valve stem.

12. A pump according to claim 11, wherein a sealing member is supported by each valve member so as to be disposed between the respective valve member and valve seat when the valve is closed.

13. A pump according to claim 12, wherein each said sealing member is an elastomeric O-ring and is supported within an annular groove defined by the respective valve head.

14. A pump according to any one of claims 11 to 13, wherein each valve means includes a valve spring which tends to hold the respective valve member in the closed position, each valve spring being helical and disposed around the respective valve stem in a state of compression between a central portion of the respective carrier member and an abutment provided on the valve stem.

15. A pump according to claim 14, wherein said abutment on each valve stem comprises a star washer pushed onto the end of the respective valve stem.

16. A pump according to any preceding claim, wherein the piston is a moulded member and is moulded onto the end of a piston rod which extends from the cylinder and which is used to effect movement of the piston within the cylinder.

17. A valve, comprising a valve member supported by a carrier member, the carrier member defining a valve seat for the valve member, wherein the valve member can be supported by the carrier member in either a first orientation so as to permit fluid to flow in one direction relative to the carrier member, or a second orientation so as to permit fluid to flow in the opposite direction relative to the carrier member.

18. A valve according to claim 17, wherein the carrier member is generally cylindrical and has an internal surface which tapers inwardly from each axial end of the carrier member so as to define a first generally conical surface at one end of the axial member and a second generally conical surface at the other end of the carrier member, the first conical surface providing a valve seat for the valve member when in the first orientation and the second conical surface providing a valve seat for the valve member when in the second orientation.

19. A valve according to claim 17 or claim 18, wherein the valve member is a poppet valve defining a valve head and a valve stem, and carries a sealing member disposed so as to lie between the valve member and the valve seat when the valve is closed.

20. A valve according to claim 19, wherein the sealing member is an elastomeric O-ring and is supported within an annular groove defined by the valve head.

21. A valve according to claim 19 or claim 20, wherein a helical valve spring is disposed around the valve stem in a state of compression between a central portion of the carrier member and an abutment provided on the valve stem, said valve spring tending to hold the valve member in the closed position.

22. A valve according to claim 21, wherein said abutment on the valve stem comprises a star washer.

23. A pump, comprising a cylinder through which pumped fluid flows, the cylinder having two axially spaced apart radially outwardly extending annular flanges, at least one of said flanges being moveable relative to the cylinder so as to vary the axial separation of the flanges, an outer cylindrical casing disposed around the cylinder between the two flanges so as to define an annular chamber around the cylinder to receive cooling fluid, and compression seals disposed between the two flanges and respective axial ends of the outer casing.

24. A pump according to claim 23, wherein the or each moveable flange can be mounted on the cylinder in a predetermined position such that the compression seals are compressed to a desired amount to provide a fluid tight seal between the outer casing and the flanges.

25. A pump according to claim 24, wherein the cylinder is provided with an abutment which limits the axial movement of the or each moveable flange so that when the or each moveable flange abuts against the or each abutment the flanges are at a minimum axial separation and the compression seals are compressed by a desired amount to provide a good fluid tight seal between the outer casing and the flanges.

26. A pump according to any one of claims 23 to 25, wherein the outer casing is held in position relative to the cylinder by the flanges.

27. A pump according to anyone of claims 23 to 26, wherein each flange is provided with an annular groove to receive a respective compression seal and a respective axial end of the outer casing.

28. A pump according to anyone of claims 23 to 27, wherein the or each moveable flange is in screw-threaded engagement with the cylinder.

29. A pump according to anyone of claims 23 to 28, wherein the cylinder comprises a generally cup-shaped body portion and an end cap, and the or at least one moveable flange is defined by the end cap.

30. A pump according to claim 29, wherein the flange not defined by the end cap is not moveable and is formed integrally with the cylinder.

31. A pump according to claim 29 or claim 30, wherein the end cap defines an inlet port for pumped fluid to enter the cylinder.

32. A pump, comprising a cylinder having an inlet port and an outlet port, wherein the cylinder comprises a generally cup shaped body portion and an end cap.

33. A pump according to claim 32, wherein an annular compression seal is disposed between the end cap and the cylinder body portion.

34. A pump according to claim 33, wherein the end cap can be mounted on the cylinder body portion in a predetermined position in which the compression seal is compressed by a desired amount te provide a good fluid tight seal.

35. A pump according to claim 34, wherein the end cap is in screwthreaded engagement with the cylinder body portion, and the cylinder body portion is provided with an abutment whereby screwing the end cap up to the abutment puts the compression seal under a desired amount of compression to provide a good fluid tight seal between the end cap and the cylinder body portion.

36. A pump according to any one of claims 32 to 35, wherein the cylinder body portion is a moulded plastics component.

37. A pump according to any one of claims 32 to 36, wherein the end cap is a moulded plastics component.

38. A pump according to any one of claims 32 to 37, wherein the end cap defines the inlet port.

39. A pump according to claim 38, wherein a one way valve is mounted in the end cap to allow fluid to flow into the cylinder.

40. A pump, substantially as hereinbefore described, with reference to Figs. 2 to 8b of the accompanying drawings.

41. A valve, substantially as hereinbefore described, with reference to Figs. 2, 6a, 6b, 7a, 7b, 8a and 8b of the accompanying drawings.