AU2016202203A1

AU2016202203A1 - Diaphgram valve guiding assembly

Info

Publication number: AU2016202203A1
Application number: AU2016202203A
Authority: AU
Inventors: Philip John Collins
Original assignee: Hansen Developments Ltd
Current assignee: Hansen Developments Ltd
Priority date: 2010-06-04
Filing date: 2016-04-08
Publication date: 2016-05-05
Anticipated expiration: 2031-06-03
Also published as: AU2016202203B2; NZ603309A; AU2011202636A1; NZ585948A

Abstract

- 14 The invention relates to a diaphragm valve and in particular to a guiding assembly for a diaphragm element within the valve and to a float type valve and in particular to a sealing arrangement for the valve. The guiding assembly of the invention comprises a guide pin and a guide bush of harder material than the soft diaphragm to reduce friction as the diaphragm moves up and down the pin to close and open the valve. The sealing arrangement of the invention comprises a rim about a hole in the valve body where the float arm seal opens and closes the valve for reducing or eliminating potential water hammer issues during wave action.

Description

- 1 DIAPHRAGM VALVE GUIDING ASSEMBLY FIELD OF THE INVENTION The invention relates to a diaphragm valve and in particular to a guiding assembly for a diaphragm element within the valve and/or relates to a float type valve and in particular to a sealing arrangement for the valve. BACKGROUND OF THE INVENTION Diaphragm valves of various types are known and used in various applications. US patent 6,374,855 describes one form of diaphragm valve. It is desirable to improve the functionality of such commonly used valves. Float valves of various types are also known and used in applications where water level needs to be maintained, such as in water troughs. It is therefore an object of the present invention to provide an improved or at least alternative form of diaphragm valve, and/or to provide an improved or at least alternative form of float valve. STATEMENTS OF THE INVENTION In a first aspect the invention may broadly be said to consist of a diaphragm valve comprising: a hollow body having a first port to connect a hydraulic or pneumatic system to the interior of the body of the valve and a second port to the interior of the body of the valve, a diaphragm movably mounted within the interior of the body and normally closing said first port, the diaphragm including side walls and a thin flexible annular skirt extending from the periphery of the diaphragm and integrally formed with the diaphragm, the distal edge of said skirt being sealingly retained around a cavity formed on one side of the diaphragm, to movably mount the diaphragm within the interior of the body of the valve so that the diaphragm moves by flexing and/or folding of the skirt, a guide pin extending through the cavity and an opening of the diaphragm and having a varying diameter along a guide length of the pin, and a guide bush of relatively harder material than the softer diaphragm retained within the opening and around the guide pin to form a channel therebetween, the channel traversing through the diaphragm from said first port into the cavity such that when the pressure in said cavity falls below the pressure on an opposing side of the diaphragm to the cavity, the diaphragm and bush will move away from said first port along the pin to open said first port to - 2 the interior of the body of the valve and will move to close said first port when the pressure in said cavity is equalised with the pressure on the opposing side of the diaphragm. Preferably the diaphragm valve further comprises a biasing member within the body for biasing the diaphragm towards said first port. Preferably the biasing member is a compression spring located within the cavity and acting on the diaphragm to bias the diaphragm towards said first port. Preferably the guide bush comprises a flange at an end of the bush arranged to engage an end of the diaphragm to retain the bush within the opening of the diaphragm. Preferably the diaphragm further comprises an annular insert of relatively harder material than the diaphragm to which the diaphragm engages about and said annular insert having one end retained within an internal flange of the diaphragm and another end retained between the diaphragm and the guide bush for providing structural support to the diaphragm. Preferably the diaphragm is moulded over the annular insert. Preferably the diaphragm is formed from a rubber material and the insert is formed from a harder plastics material. Preferably, the hollow body comprises a main body component and a cap mounted at an end of the main body component so that the cavity is defined between the inside face of the cap and diaphragm, the distal edge and the inside face of the cap having complimentary formations to retain the distal edge of the skirt against the inside face of the cap. Preferably, the guide pin extends centrally from the inside face of the cap through the cavity and opening of the diaphragm. Preferably, the guide pin extends 1 to 1.5 mm into said first port and beyond the opening in the diaphragm when the diaphragm is closing said first port. Preferably, the cap comprises a cover arranged to engage the hollow body at one end to define the cavity and a cap element arranged to threadably engage the body over the cover to thereby retain the cover in place. Preferably the valve further comprises a hole in the body adjacent the cavity sized to allow greater fluid flow from the cavity through to the exterior of the valve than through the channel - 3 when the hole is open, thereby causing the pressure in the cavity to fall below the pressure on the other side of the diaphragm to open the valve, and wherein fluid flow to the exterior of the body from the cavity is prevented when the hole is closed allowing pressure in the cavity to equalise with the pressure on the other side of the diaphragm to close the valve. In a preferred embodiment, the valve is a float valve further comprising a float arm adjacent the hole at one end and adaptable to be coupled to a float at another end, the arm being pivotally coupled to the body of the valve so that pivotal movement of the arm due to movement of the float causes the end adjacent the hole to open and close the hole. Preferably the diaphragm valve further comprises a rim projecting from the body about the hole for engaging a resilient sealing member of the float arm, the rim having at least one opening such that in a first pivotal position of the float arm the sealing member contacts the rim without closing the hole thereby enabling fluid to flow from the hole through the opening of the rim to the exterior of the valve, and further pivotal movement of the float arm to the closed position causes the sealing member to compress against the rim and move towards the hole to close the hole and prevent fluid from flowing from the cavity to the exterior of the valve. Preferably the rim comprises a plurality of annular projections spaced around the hole in the body. Preferably the hole and rim are formed in the cover of the cap. Preferably the guide pin is of a relatively greater diameter at an end of the pin adjacent the first port and of a relatively smaller diameter within the cavity to thereby decrease the channel width when the diaphragm moves to close the valve and increase the channel width when the diaphragm has moved away from said first port respectively. The term "comprising" as used in this means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

- 4 BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be described by way of example only and with reference to the drawings, in which: Figure 1 is a perspective view of a first embodiment of a diaphragm valve of the invention, Figure 2 is a cross-sectional view of the valve of figure 1 shown in the closed position, Figure 3 is a cross-sectional view of the valve of figure 1 shown in the open position, and Figure 4 is an enlarged view of the guiding assembly of the valve of figure 2, Figure 5 is a cross-sectional view of an embodiment of the valve of figure 1 employing a biasing spring and an alternative sealing arrangement and shown in the open position, Figure 6 is a cross-sectional view of the valve of figure 5 shown in the open position with the float arm pivoted towards the closed position due to wave action, Figure 7 is an enlarged view of the sealing arrangement of the valve in figure 6, Figure 8 is a cross-sectional view of the valve of figure 5 shown in the closed position, and Figure 9 is an enlarged view of the sealing arrangement of the valve in figure 8. DETAILED DESCRIPTION Referring to figure 1 a diaphragm valve 100 of the invention is shown. The valve 100 is a float type valve having a main body 10 and a float arm 20 coupled to the main body 10 and a diaphragm assembly within the body 10 for actuating the valve 100, to open and close the fluid path between inlet and outlet ports 11 and 12 respectively. Referring now to Figures 2 and 3, the main body 10 has a hollow interior 15, an inlet port 11 by which the diaphragm valve 100 may be connected to a pipe system from a fluid supply under pressure for example, and an outlet port 12 which may also connect to a pipe system or directly communicate with a trough or reservoir for example. The inlet port 11 is formed by an aperture at end 10a of the body opposite end 10b. The aperture is internally threaded so that the valve 100 may be threaded onto the end of a pipe for example so that the end of the pipe - 5 communicates through the inlet port 11 and into the interior 15 of the valve 100. Outlet port 12 is provided for the exit stream of fluid from the interior 15 of the body 10 of the valve 100. Fluid will enter through inlet port 11 and flow through the interior 15 of the valve 100, exiting via outlet port 12 only when the valve 100 is open (as shown by stream C in figure 3). When the valve 100 is closed, the fluid path is obstructed and the outlet port 12 is closed so no fluid exits the valve 100. A circular wall 30 extends from the inlet port 11 into the interior 15 of the valve as shown, and terminates at one end to form a valve seat 11a. A diaphragm 7 is mounted within the interior 15 of the valve. In the preferred form the diaphragm 7 is generally circular, and comprises a thin annular skirt 7a which extends from the periphery of the side wall 7b of the preferred form diaphragm 7 as shown. The distal edge 7c of the skirt 7a and the inner surface of end 10b both comprise complementary formations 8 (such as a recess at the inner surface of end 10b for receiving distal edge 7c) for retaining the distal edge 7c against/within the inner surface of end 10b. In the preferred embodiment shown, the hollow body 10 comprises a main body component 10 and a cap element 29 mounted at end 10b of the body 10. The cap element 29 having a formation 8 formed on the inside face for retaining the diaphragm 7. The cap element 29 in the preferred embodiment is shown as two separate components, a cover 29a engaging the main body component 10 at end 10b and a cap 29b threadably engaging the main body component 10 over the cover 29a to retain the cover at end 10b. In an alternative embodiment however the cap element 29 may be a single component. The cover 29a and cap 29b will be referred to as cap or cap element 29 from here onwards. The skirt 7a is a thin, flexible skirt which can flex and fold to allow the diaphragm 7 to move between the position shown in figure 2 where the diaphragm 7 seals against the seat 11a to close the outlet port 12, and the position shown in figure 3 where the diaphragm 7 has moved towards the cap 29 to open the port 12, to the interior 15 of the body 10. The diaphragm 7 is preferably a separately moulded plastic component which is simply fitted to body 10 so that the edge 7c of the skirt 7a of the diaphragm 7 enters into the annular formation 8 in the body and the diaphragm 7 is not secured by screws or clamps or similar. This provides for easy assembly and a simple construction and moreover it has been found that the diaphragm 7 will effectively seal for both vacuum and pressure, up to relatively high pressures. In one form, the diaphragm 7 including the integral skirt 7a are formed from a soft plastics material and the diaphragm 7 has a side wall 7b and an annular flange 7d extending inwardly - 6 from the side wall 7b for receiving an annular member/insert 17 of harder material. The annular flange 7d having an orthogonal base and wall structure for receiving an end of member 17 therein. The member/insert 17 has a similar profile to the diaphragm 7 to allow the diaphragm 7 to lie against the member/insert 17 as shown and move up and down the body 10 with the member 17 to open and close the valve 100. Member/insert 17 aids the soft diaphragm 7 in keeping its structure as it moves up and down the body 10. However member/insert 17 is only a preferable feature and may not be employed in some embodiments. Another annular member 18 fitted or otherwise integrally formed within the main body 10 of the valve 100 engages an upper surface of a flange 7e extending from the end 7c of the skirt 7a above the annular formation 8 to hold the flange 7e against the formation 8 and allow the thin skirt 7a to fold/flex to move the diaphragm 7 to open the valve 100 as shown in figure 3. In the preferred embodiment, the diaphragm 7 is formed from a rubber material and over moulded onto the annular member/insert 17. A guide member 22 extends centrally from the cap 29 through an aperture or opening 21 in the centre of the diaphragm 7 and towards the port 11. The guide member 22 may be formed as a separate component from the body 10 and received within a recess 23 of the cap 29 as shown. In the preferred form the guide member is a cylindrical pin 22. Referring now to Figure 4, a guide bush 24 is accommodated within the opening 21 at end and has a main body component 24a inside the diaphragm 7 and a flange 24b at an end of the body 24a engaging the end of the diaphragm at opening 21. The guide pin 22 extends through the centre of the bush 24 as shown. The bush 24 around the pin 22 is slightly larger than the diameter of the pin 22 and forms a channel 26 through the diaphragm from the port 11 to the cavity or space 25 behind the diaphragm (shown in Figures 2 and 3), between the rear side of the diaphragm and the cap 29 of the body. The guide bush 24 is formed from a harder material than the soft diaphragm 7 to thereby reduce friction as the diaphragm 22 moves up and down the pin 22. Preferably the guide bush 24 is formed from a plastics material. The guide bush 24 may be formed separately or integrally moulded with the diaphragm and/or member/insert 17. The guide pin 22 is preferably of a length such that it extends past the bush 24 and opening 21 when the diaphragm 7 is in the open and closed positions (as shown in figure 4). For example, the pin 22 may extend 1-1.5mm past the bush 24 when the diaphragm is in the closed position. This arrangement helps prevent the channel 26 from getting blocked. As the pin 22 is always protruding through and out the bush 24, it will act to push any debris out and away from channel 26 when the diaphragm moves along the pin 22. Furthermore, the guide bush 24 is preferably only slightly larger than the pin 22 to prevent large particles from getting - 7 into and blocking the channel 26. This small size difference means only small debris particles can enter through channel 26 which also prevents hole 27 through cap 29 from getting blocked due to the relative size difference between the channel 26 and the hole 27 (explained in more detail further below). Referring now also to Figures 2 and 3, the preferred form valve shown has a hole 27 formed through the cap 29 adjacent the cavity 25. Hole 27 when opened enables fluid to flow from the cavity 25 to the exterior of the valve and is sized to allow greater flow than through the channel 26. A seal 28 at the end of the float arm 20 is situated adjacent the hole 27 to open and close the hole 27 with pivotal movement of the arm 20. Seal 28 is preferably made of rubber to provide the necessary sealing against hole 27 when the valve 100 is closed. In operation, when the float arm 20 pivots to the open position shown in figure 3 there will be a reduction in pressure via the hole 27 in the cavity 25 behind the diaphragm 7 and relative to the inlet port side of the diaphragm 7. This relative pressure imbalance will cause the diaphragm 7 to move towards the cap 29 from the position shown in figure 2 to that shown in figure 3, thus opening the outlet port 12 to the interior 15 of the body 10 to allow fluid to pass from the inlet port 11 through to the outlet port 12 as indicated by arrow C. Fluid from the inlet port 11 will operate against the top surface of the diaphragm 7 to move the diaphragm towards cap 29 further thereby increasing fluid flow through the valve 100. When the float arm 20 pivots to the closed position as shown in figure 2, fluid flow through hole 27 will be prevented/blocked off causing pressure within the cavity 25 to build up through channel 26 to thereby equalise with the inlet port side of the diaphragm 7. This equalisation of pressure alongside the natural resilience of the thin flexible skirt 7a of the diaphragm will cause the diaphragm 7 to move back up to its original position against seat 11a to close the outlet port 12 off from the inlet 11 as shown in figure 2. The hole 27 is sized to allow greater fluid flow than through channel 26. Guide bush 24 aids with this requirement by providing an aperture at opening 21 that is only slightly larger than the diameter of the guide pin 22. Channel 26 will therefore have a small width to restrict flow from the inlet side of the diaphragm to the cavity 25 to enable pressure reduction in the cavity 25 when the valve 100 (and hole 27) is opened. For example the diameter of channel 26 may be approximately 1.9mm, the diameter of the guide pin may be approximately 1.6mm and the diameter of the hole 27 may be approximately 1.9mm. These dimensions are only exemplary and are not intended to be limiting.

- 8 For the float type valve of the preferred embodiment, the float arm 20 is generally connected to a float element (not shown) arranged to float within a fluid reservoir such as a water trough for example. As the level of fluid in the reservoir lowers, the float element pulls the float arm 20 which unblocks hole 27 and causes the valve 100 to open. Water can then flow from an external source through inlet 11 and out port 12 into the trough. Once the desired level is reached, the weight of the float element no longer forces the float arm 20 to pivot downwards which then causes the float arm 20 to pivot back and block the hole 27 to close the valve 100. As shown in the figures, the pin 22 is of a constant diameter throughout its length. In an alternative embodiment however, the pin 22 may be formed with a varying diameter along its length. For instance, the diameter of the pin 22 may decrease at the lower portion adjacent the bush 24 when the diaphragm 7 is in the open position. This means the width of channel 26 will increase when the diaphragm 7 moves to the open position. When the valve 100 is caused to close, the increased size of channel 26 will allow a greater flow of fluid through to the cavity 25 allowing a faster pressure build up behind the diaphragm 7 and thereby speeding up the closing action of the valve 100. The diameter of the pin 22 will be greater at the upper portion adjacent the bush 24 when the diaphragm 7 is in the closed position, decreasing the width of the channel 26 relative to hole 27 to prevent blockage and enable proper operation of the valve 100 as described above. Referring to figures 5 and 8, in one embodiment the valve 100 further comprises a spring element 40 or other biasing means fitted between the diaphragm 7 and the cap 29 in cavity 25 to assist in moving the diaphragm towards the closed position. Figure 8 shows the spring element 40 in a less compressed/relaxed state and pushing the diaphragm 7 (and in particular acting on the relatively harder member 17) up against the valve seat 11a to close the valve 100. Figure 5 shows the valve 100 in the open position, with the member 17 acting against the top of the spring 40 to compress the spring 40 and thereby bias the diaphragm 7 towards the closed position. The embodiments shown in figures 1 - 9 are for a float valve. However other type valves may employ the diaphragm structure of the invention. In particular, the soft diaphragm 7 alongside the harder guide bush 24 and guide pin 22 provides a low friction valve for enhanced operation. As such, any type valve having a diaphragm that is caused to move due to pressure difference or equalisation to open or close the valve will benefit from this low friction guiding assembly and the scope of the invention is not intended to exclude such other type valves. Furthermore, diaphragm valves of the invention may be formed in large and small sizes. Because the valve comprises relatively few components it is inherently robust and reliable in - 9 operation, and all the components of the valve maybe formed by injection moulding, or by metal casting for larger versions if desired. In the case of a float valve, wave action within a reservoir can disrupt the operation of the valve. This wave action could be caused by wind, by water flow from the valve outlet or by stock drinking from the trough for example. This causes the float to move up and down uncontrollably which could in turn cause the float arm 20 to move and the seat/seal 28 to open and close the hole 27 in the body of the valve 100. Consequently, this results in the diaphragm 7 opening and closing the valve 100 rapidly leading to potential water hammer issues. Referring now to figures 5-9 an alternative sealing arrangement (generally indicated as 50 in figures 5, 6 and 8) about hole 27 is shown. The particular sealing arrangement 50 dampens the rapid operation of the float arm 20 due to wave action. As shown in more detail in figure 7 and 9, a rim 51 projects from the cap 29 around the hole 27. The rim 51 has at least one opening 52(in the form of an aperture or a gap for example) for fluid to flow through. In the preferred form shown, the rim 51 comprises one or more arcuate protrusions/projections (51a, 51b and 51c in figures 7 and 9) extending from the cap 29 around the hole 27. Any number of protrusions/projection 51a/51b/51c can be employed provided they are separated such that at least one gap 52 is provided in the rim 51 for fluid to flow through. The end of each protrusion/projection 51a/51b/51c (or the end of the rim 51) projects past the level at which the hole 27 lies to enable contact with the seal 28 prior to closure of the hole 27. As shown in figure 6 and in particular figure 7, when the float is bouncing in the water due to wave action, the rim 51 contacts the seal 28 and prevents the seal 28 from contacting and closing the hole 27. The seal 28 in this instance would sit on the rim 51(when fluid level has risen slightly due to wave action) but not compress enough to close hole 27. In other words, the wave does not provide sufficient force on the float arm 20 to pivot it enough to compress the seal 28 against the rim 51 to a level where it contacts against and closes the hole 27. In the case of the preferred embodiment, the seal 28 is shown resting on and slightly compressed against protrusions 51b and 51c, but is well clear of the hole 27. Fluid will therefore continue to flow through the hole 27 and through the opening(s) 52 in the rim 51to maintain an open valve 100. As shown in figure 8 and in particular figure 9, when there is sufficient force to pivot the float arm 20 towards the closed position (due to rising fluid level in the reservoir) the float arm 20 compresses the seal 28 further against the rim 51 until the seal 28 contacts against the hole 27 to close the hole 27. This will in turn close the valve 100 as described above. The seal 28, - 10 preferably being made from a compressible material such as rubber material, therefore acts as a dampening member as well as a sealing member in the valve 100. The sealing arrangement 50 of figures 5-9 is shown used in a diaphragm valve. However, such an arrangement is suitable for any float type valve where wave action or similar affects or degrades the operation of the valve. As such, a float valve having a hole in the body and a corresponding seal that controls opening and closing of the valve can benefit from such an arrangement and the invention is not intended to exclude such valves. The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention as defined by the accompanying claims.

Claims

1. A diaphragm valve comprising: a hollow body having a first port to connect a hydraulic or pneumatic system to the interior of the body of the valve and a second port to the interior of the body of the valve, a diaphragm movably mounted within the interior of the body and normally closing said first port, the diaphragm including side walls and a thin flexible annular skirt extending from the periphery of the diaphragm, the distal edge of said skirt being sealingly retained around a cavity formed on one side of the diaphragm, to movably mount the diaphragm within the interior of the body of the valve so that the diaphragm moves by flexing and/or folding of the skirt, a guide pin extending through the cavity and an opening of the diaphragm and having a varying diameter along a guide length of the pin, and a guide bush of relatively harder material than the softer diaphragm retained within the opening and around the guide pin to form a channel therebetween, the channel traversing through the diaphragm from said port into the cavity such that when the pressure in said cavity falls below the pressure on an opposing side of the diaphragm to the cavity, the diaphragm and bush will move away from said first port along the pin to open said first port to the interior of the body of the valve and will move to close said first port when the pressure in said cavity is equalised with the pressure on the opposing side of the diaphragm.

2. A diaphragm valve as claimed in claim 1 further comprising a biasing member within the body for biasing the diaphragm towards said first port.

3. A diaphragm valve as claimed in claim 2 wherein the biasing member is a compression spring located within the cavity and acting on the diaphragm to bias the diaphragm towards said first port.

4. A diaphragm valve as claimed in any one of the preceding claims wherein the guide bush comprises a flange at an end of the bush arranged to engage an end of the diaphragm to retain the bush within the opening of the diaphragm.

5. A diaphragm valve as claimed in claim 4 further comprising an annular member of relatively harder material than the soft diaphragm to which the diaphragm engages about and said annular member having one end retained within an internal flange of the diaphragm and another end retained between the diaphragm and the guide bush for providing structural support to the diaphragm. - 12

6. A diaphragm valve as claimed in claim 5 wherein the diaphragm is formed from a rubber material, the annular member is formed from a harder plastics material, and the diaphragm is integrally moulded over the annular member.

7. A diaphragm valve as claimed in any one of the preceding claims wherein the hollow body comprises a main body component and a cap mounted at an end of the main body component so that the cavity is defined between the inside face of the cap and diaphragm.

8. A diaphragm valve as claimed in either one of claim 6 or claim 7 wherein the distal edge and the inside face of the cap comprise complimentary formations to retain the distal edge of the skirt against the inside face of the cap.

9. A diaphragm valve as claimed in any one of claim 6 to claim 8 wherein the guide pin extends centrally from the inside face of the cap through the cavity and opening of the diaphragm.

10. A diaphragm valve as claimed in any one of the preceding claims wherein the guide pin extends 1 to 1.5 mm into said first port and beyond the opening in the diaphragm when the diaphragm is closing said first port.

11. A diaphragm valve as claimed in any one of claim 6 to claim 10 wherein the cap comprises a cover arranged to engage the hollow body at one end to define the cavity and a cap element arranged to threadably engage the body over the cover to thereby retain the cover in place.

12. A diaphragm valve as claimed in any one of the preceding claims further comprising a hole in the body adjacent the cavity sized to allow greater fluid flow from the cavity through to the exterior of the valve than through the channel when the hole is open, thereby causing the pressure in the cavity to fall below the pressure on the other side of the diaphragm to open the valve, and wherein fluid flow to the exterior of the body from the cavity is prevented when the hole is closed allowing pressure in the cavity to equalise with the pressure on the other side of the diaphragm to close the valve.

13. A diaphragm valve as claimed in claim 12 wherein the valve is a float valve further comprising a float arm adjacent the hole at one end and adaptable to be coupled to a float at another end, the arm being pivotally coupled to the body of the valve so that pivotal - 13 movement of the arm due to movement of the float causes the end adjacent the hole to open and close the hole.

14. A diaphragm valve as claimed in claim 13 further comprising a rim projecting from the body about the hole for engaging a resilient sealing member of the float arm, the rim having at least one opening such that in a first pivotal position of the float arm the sealing member contacts the rim without closing the hole thereby enabling fluid to flow from the hole through the opening of the rim to the exterior of the valve, and further pivotal movement of the float arm to the closed position causes the sealing member to compress against the rim and move towards the hole to close a fluid passage between the hole and the opening to prevent fluid from flowing from the cavity to the exterior of the valve.

15. A diaphragm as claimed in claim 14 wherein rim comprises a plurality of arcuate projections spaced around the hole in the body.

16. A diaphragm valve as claimed in either one of claim 13 or claim 14 wherein the hole and rim are formed in the cover of the cap.

17. A diaphragm valve as claimed in any one of claim 1 to claim 16 wherein the guide pin is of a relatively greater diameter at an end of the pin adjacent the first port and of a relatively smaller diameter within the cavity to thereby decrease the channel width when the diaphragm moves to close the valve and increase the channel width when the diaphragm has moved away from said first port respectively.

18. A valve substantially as described herein with reference to accompanying figures 1 to 4.