WO1998006910A1

WO1998006910A1 - Improved mains pressure flusher valve

Info

Publication number: WO1998006910A1
Application number: PCT/AU1997/000508
Authority: WO
Inventors: Stephen Archibald Hill
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-08-13
Filing date: 1997-08-13
Publication date: 1998-02-19
Anticipated expiration: 1999-02-13
Also published as: AUPO160596A0; ID18028A; TW374810B

Abstract

A mains pressure flusher valve (10) which includes a valve body (8) defining (i) a main chamber (12) having a main inlet for fluid and a main outlet for fluid (9) and (ii) a discharge chamber (14) extending downstream from the main outlet (9), the discharge chamber (14) being adapted to be connected in use to a flush pipe (48); a piston (17) located in the main chamber (12) which is movable into and out of sealing engagement with the main outlet (9); a non-return valve (36) located in the discharge chamber (14) having a mouth at its upstream inlet and a outlet, the non-return valve (36) adapted to inhibit fluid flowing from the downstream side of the non-return valve (36) to any part of the mains pressure flusher valve upstream of the non-return valve; sealing means (46) to inhibit fluid in the discharge chamber (14) from escaping, in use, to an external surface of the flush pipe (48); a subsidiary passageway (13) having (i) a first portion with an entry for fluid in fluid communication with an upper portion (40) of the main chamber (12) above the piston (17), (ii) a control valve to permit flow of fluid through the subsidiary passageway (13) and (iii) a second portion (13a) adjacent to the discharge chamber with an outlet for fluid into the discharge chamber (14), the outlet for fluid located downstream of the main outlet (9) and upstream of, and spaced from, the sealing means (46).

Description

IMPROVED MAINS PRESSURE FLUSHER VALVE

Field

The invention relates to mains pressure flusher valves. In particular, it has application to mains pressure flusher valves in which the valve is opened and closed by the flow of fluid through a subsidiary passageway.

Background

The prior art describes valves which are controlled by the flow of the same fluid which is controlled by the valve. Typically, these valves rely upon the pressure of fluid at an inlet point being in some way diverted such that it applies pressure on the valve-head so as to urge the valve into a closed position. The valve includes a release mechanism such that the pressure which holds the valve closed can be released, thereby opening the valve. The valves typically close automatically once the initial release mechanism is deactivated. Valves of this type are described in, among other documents, international patent application PCT/AU93/00046 (W093/ 16240). This specification describes a simpler valve than that of the prior art which can be used at mains water pressure, which had not previously been described. That specification is expressly incorporated into this specification by reference and this specification is intended to be read in conjunction with that specification.

Where such valves are used to control water for flushing a toilet, a common requirement of flusher valves is that they are not susceptible to back siphonage. In other words, if a vacuum pressure is applied to main inlet, the valve must include a means to inhibit fluid being sucked back through the valve in the reverse direction to normal flow. This may be achieved by providing venting holes or air-vents in the valve to permit the entry of air into the valve. Accordingly, if a vacuum is applied upstream of the junction, air will be sucked in through the air-vents rather than fluid from the flush pipe. However, the valve must be constructed so that while air can enter into the valve, the same openings or air- vents do not permit water or other fluid to escape or leak from the valve.

Such a valve may include a non-return valve located adjacent to the outlet of the main chamber to further inhibit water from the toilet being drawn back through the valve into a mains pressure system. In particular, it is known to use a resilient deformable material, such as rubber. These types of non-return valves include a longitudinal slit at the end of converging walls Accordingly, water flowing in the direction of the convergence has sufficient pressure to open the slit and continue flowing, whereas water flowing in the opposite direction is unable to open the slit

A valve embodying the invention described in the specification of international patent application PCT/AU93/00046 is shown in figure 1 The operation of the valve is described in the specification This valve has some disadvantages which are better understood after describing part of the valve in some detail The valve body disclosed in that specification has a primary and a secondary recess at its lower end at the top of discharge chamber 14 but below main chamber 12. The recesses are defined by walls 4 and 5 respectively to form a "stepped" structure down from valve seat 18a The internal diameter of the valve body at valve seat 18a therefore becomes one step larger at the secondary recess (formed by wall 5) and then larger again at the primary recess (formed by wall 4) Located in the secondary recess at the junction of the main outlet passageway and the subsidiary passageway is a "venting insert" 2, being the annular element surrounding the depending projection from piston 17 Adjacent venting insert 2 is a groove 6 in the annular surface (or "step") joining walls 4 and 5 Although not immediately apparent from the perspective shown in figure 1 , subsidiary passageway 13 ends in an aperture above wall 4 at one end of groove 6 (the left end as seen in figure 1 ) Groove 6 forms a channel with the upper surface of the non-return valve 36 and thereby connects the aperture at the end of passageway 13 with an annular groove 7 in venting insert 2. Drain channels 1 in venting insert 2 provide a channel for fluid into non-return valve 36. Fluid flows in use from the aperture along the channel 6 (across the top of the upper surface of the non-return valve 36) to the channel 7 around venting insert 2 and then drains around the side of the venting insert through drains 1 into non-return valve 36.

At least two problems have been experienced with this type of valve in use The first is the potential for obstacles to develop in the path of fluid from passageway 13, particularly in groove 6 along the top of the rubber surface of the on-return valve As a result of the limited flow, there is a resistance to the emptying of subsidiary passageway 13 (and therefore upper chamber 40) This unevenness in flow will prolong the flush which would result in a wastage of water and uneven closing of the valve It may also cause water hammer upon operation of the valve, or substantial hydraulic vibrations within the mains pressure system to which the valve is connected. Depending on the pressure of the system, this may be very serious and is generally undesirable.

A second problem relates to the need to ensure as good a seal as possible at the junction of outlets in the discharge chamber to minimise any leakage of water. This is particularly important where the valves may be installed in water-sensitive locations, such as behind walls where they may cause damage to the building if water leaks out. In the valve described in PCT/AU93/00046, fluid can leak around the top of the non-return valve 36 shown in Figure 1 from groove 6 and then escape through air-vents 38, or along the external surface of flush-pipe 48 or elsewhere. Air-vents need to be as small as possible to minimise leaks but as large as possible to maximise back-siphonage protection.

Further problems have been found with the rubber of the non-return valve blocking, or partially blocking, some of the smaller passageways for fluid around it, such as the drains 1 where there are slight unevennesses in the surface of the non-return valve (which often occur as rubber is naturally not as precise a material to work with compared with brass). It has also been found to be desirable to have one valve which can easily be used to fit to different diameter flush pipes. A further problem has been that the venting insert 2 is a small and easily damaged component which will easily fall out upon disassembly in situ.

Accordingly, investigations have been carried out to provide such a valve with improved leakage resistance and more smooth closing and effective back-siphonage protection and multi-size flush-pipe fit, while keeping the valve simple in construction and minimise the number of components.

Summary of the invention

According to the invention, there is generally provided a mains pressure flusher valve which includes: a valve body defining (i) a main chamber having a main inlet for fluid and a main outlet for fluid and (ii) a discharge chamber extending downstream from the main outlet, the discharge chamber being adapted to be connected in use to a flush pipe; a piston located in the main chamber which is moveable into and out of sealing engagement with the main outlet; a non-return valve located in the discharge chamber having a mouth at its upstream inlet and an outlet, the non-return valve adapted to inhibit fluid flowing from the downstream side of the non-return valve to any part of the mains pressure flusher valve upstream of the non-return valve; sealing means to inhibit fluid in the discharge chamber from escaping, in use, to an external surface of the flush pipe; a subsidiary passageway having (i) a first portion with an entry for fluid in fluid communication with an upper portion of the main chamber above the piston, (ii) a control valve to permit flow of fluid through the subsidiary passageway and (iii) a downstream end portion adjacent to the discharge chamber with an outlet for fluid into the discharge chamber downstream of the main outlet and upstream of, and spaced from, the sealing means.

Preferably, the valve body wholly defines the end portion of the subsidiary passageway.

Preferably, the sealing means includes an annular surface of the valve body around the discharge chamber normal to the direction of fluid flow, in use, through the valve body co-operating with a resilient flange on the non-return valve to form a seal. More preferably, the sealing means further includes a flush pipe adaptor which engages the valve body to hold the resilient flange against the valve body.

In another preferred embodiment, the flush pipe adaptor further includes elongate apertures adapted to permit air to flow into the flush pipe, the apertures being located downstream of the non-return valve but, in use, located above the non-return valve outlet such that fluid downstream of the non-return valve is directed by gravity away from the apertures.

The non-return valve is preferably constructed of a resilient flexible material such that greater flow of fluid through the outlet causes the non-return valve to expand to permit a greater flow rate of fluid through the non-return valve. Preferably, the piston has an internal passageway which communicates between an upper portion of the main chamber and the inlet and the non-return valve is adapted to provide resistance to fluid flowing therethrough to increase the pressure of fluid at the inlet of the internal passageway such that the non-return valve cooperates with the internal passageway to generate sufficient flow of fluid through the internal passageway during movement, in use, of the piston towards the main outlet to promote movement of the piston into a position of sealing engagement with the outlet. More preferably, the piston further includes at least one flow valve located in the internal passageway of the piston to regulate the passage of fluid through the internal passageway.

It is further preferred that the piston further includes a depending projection of slightly smaller diameter than the main outlet adapted to promote smooth movement of the piston into sealing engagement with the outlet.

Preferably, the valve further includes mechanical and/or electrical actuation means to actuate the control valve.

In another preferred embodiment, the valve further includes a venting insert (as defined below) in the discharge chamber, the venting insert including: an inlet located downstream of the main outlet and upstream of the subsidiary passageway outlet and adapted such that at least substantially all of fluid flowing, in use, through the main outlet flows through the venting insert inlet; an outlet downstream of the subsidiary passageway outlet; and an exterior cavity in the external surface of the venting insert adapted to form at least one channel for fluid from the subsidiary passageway outlet to the venting insert outlet.

Preferably, the exterior cavity includes a circumferential groove in an exterior surface of the venting insert, the groove being aligned in situ with the subsidiary passageway outlet, and the cavity also including at least one channel leading from the circumferential groove to the venting insert outlet. More preferably, the venting insert inlet is accommodated within an annular recess within the valve body adjacent the main outlet.

Preferably, the valve further includes a rigid non-return valve support located within the non-return valve and adapted to support the non-return valve in situ in the valve, the valve support having an upstream mouth adjacent to the mouth of the non-return valve, the valve support's mouth being adapted to co-operate with the venting insert outlet such that fluid from the main outlet and the subsidiary passageway outlet is directed into the non-return valve. Preferably, the valve support and venting insert are one piece.

In another preferred embodiment, the valve further includes piston stop means located in the upper portion of the main chamber and opposite the piston, the piston stop means being adapted to form a stop to movement of the piston, in use, away from the outlet and such that the piston stop means does not obstruct or enter the internal passageway. Preferably, the piston stop means is adjustable to control the amount of movement away from the outlet of the piston in the main chamber.

Preferably, the flush pipe adaptor has apertures adapted to permit air to flow through the apertures such that, upon (i) a first air-pressure being applied outside the valve and (ii) a second air-pressure, being less than the first air-pressure, being applied at or upstream of the main outlet, air flows through the apertures in an upstream direction through the main outlet.

It will be apparent to one skilled in the art that a number of the features of various of the preferred embodiments can be combined in one valve.

Description of the drawings

A preferred embodiment of the invention will now be illustrated by way of example only with reference to the accompanying drawings in which:

Figure 1 shows a cross-sectional view from the side of a mains pressure flusher valve in a closed position according to the invention of PCT/AU93/00046

Figure 2 shows a shows a cross-sectional view from the side of a mains pressure flusher valve in a closed position according to a first embodiment of the invention.

Figure 3 shows an enlarged side view of the venting insert shown in figure 2. Figure 4 shows a bottom view of the venting insert illustrated in figure 3.

Figure 5 shows a perspective view of the flush pipe adaptor shown in figure 2.

Figure 6 shows a side view of a venting sleeve according to another preferred embodiment of the invention for use in the valve of figure 2.

In the drawings illustrating various embodiments of the invention, for convenience only like components are given the same numerical reference. Figure 2 shows a valve 10 having a valve body 8. The inlet chamber in the embodiment shown is on the side of the valve into the page behind the valve 10 and is constructed broadly similarly to the inlet 1 1 shown in figure 1. As in figure 1, the valve body 8 of figure 2 has an annular main chamber 12, the bottom of which is adjacent to the inlet chamber and a discharge chamber 14. Running parallel beside the main chamber 12 is a smaller "subsidiary passageway" 13 which is in fluid connection with the top of main chamber 12 (being upper portion 40) and discharge chamber 14.

The main chamber 12 contains a piston 17. The piston 17 has in its lower portion an annular rubber surface 18 (in the form of an affixed washer) which engages with a corresponding seat 18a formed in the valve body 8 to form a seal when the valve is in the closed position (as shown in figure 2). This prevents water flowing from the inlet chamber to discharge chamber 14 when piston 17 is in the closed position. Piston 17 has a depending projection 39 of slightly smaller diameter than the discharge chamber 14 to form a choke as explained below. Piston 17 also has a transverse channel 19 through its lower portion in fluid communication with the inlet chamber and, extended up from that channel, an axial passageway 20 which communicates with channel 19. A filter (not shown) may be located at one end of the axial passageway 20 where it meets with the transverse passageway 19. Two small flow valves 21 and 22 are also located in the axial passageway 20 to prevent the flow of fluid from upper portion 40 through to axial passageway 20. The flow valves also regulate the amount of water permitted to flow into upper portion 40. Channel 23 is a relatively narrow extension of passageway 20 which connects valve 22 to the upper portion 40 of the main chamber 12 and is offset from the main axis of the valve so that it is not blocked by stop 30 when the valve is in the open position. In summary, water is able to flow from the inlet chamber into main chamber 12 and into transverse passageway 19, and thereafter into the axial passageway 20 through flow valves 21 and 22, and through channel 23 into the upper portion 40.

Situated above main chamber 12 is a bonnet 25 which seals the top of upper portion 40 of main chamber 12. "O"-ring 32 forms the seal. Within bonnet 25 is piston stop 30 projecting into upper portion 40, which is adjustable by bolt-head 33. To prevent leakage of water from the bonnet 25, an "O"-ring 24 is located beneath bolt head 33. The stop 30 projecting into the main chamber 12 controls the extent of upward movement of piston 17 and thus the volume of upper portion 40 when the valve is in the open position. That volume controls (as explained below) the period between actuation of the valve and the cessation of water flow through the valve.

There is a further passageway for fluid (not shown in figure 2) which leads from upper portion 40 through bonnet 25 to the top of passageway 13, via a control valve (which also is not shown). The control valve has an open and closed position at which fluid is permitted or inhibited respectively from flowing through this passageway. The operation of this valve is not relevant to the invention described in this specification and is not described in detail. A description of two of the different mechanisms available is in PCT/AU93/00046. Passageway 13 communicates at its downstream end with discharge chamber 14 via an end portion 13a of the passageway 13 formed in valve body 8, which empties into the discharge chamber adjacent the external channel 53 of venting insert 51. End portion 13a is wholly defined by a bore in valve body 8 and its outlet is an opening in wall 65.

Outlet or discharge passageway 14 is defined at its most upstream end by valve body 8 immediately downstream of main outlet 9 and valve seat 18a. Valve body 8 has a primary and a secondary recess at its lower end, defined by walls 64 and 65 respectively to form a "stepped" structure down from valve seat 18a. The internal diameter of the valve body at valve seat 18a therefore becomes one step larger at the secondary recess (formed by wall 65) and then larger again at the primary recess (formed by wall 64). Compared with the prior art valve shown in figure 1, it will be seen that secondary recess is larger and wall 65 is correspondingly taller than wall 5 of figure 1. Located in the secondary recess at the junction of the main outlet passageway and the subsidiary passageway 13 is venting insert 51, being the annular element surrounding depending projection 39 from piston 17. Thus, immediately downstream from main outlet 9, the discharge chamber is defined firstly by the internal surface of venting insert 51 and, further downstream, by the internal surface of non-return valve 36, which is in its most upstream part "lined" by non-return valve support 49. The non-return valve 36 is an elastomeric one-way valve, having converging walls at one end meeting at a slit perpendicular to the flow of fluid, such that fluid flow in one direction (down the page) along the converging walls opens the slit but fluid pressure from the other end (up the page) leaves the slit closed, hence inhibiting flow in that direction. The non-return valve has an annular flange 46 defining its upstream mouth and also defining an upper ri which rests against a smooth surface connecting annular walls 64 and 65 (being the step between the primary and secondary recesses) to form a seal with the valve body against leakage around the outside of the non-return valve 36. Non-return valve support 49 is made of brass (as is venting insert 51) and has a rim 56 which is located within an annular recess in the internal wall of flange 46 to hold the upstream part of non-return valve 36 firmly as well as holding the mouth of non-return valve 36 (distant from the slit) open and firmly in position near the main outlet 9.

Shown in greater detail in figure 3, venting insert 51 has a top flange 52 which seats with valve body 8 in outlet passageway 14. The venting insert 51 also has an external recess, including a circumferential groove 53 and drain channels 54. Drain channels 54 can be more clearly seen in figure 4 which is a bottom view of venting insert 51. When fluid flows from passageway 13a, it is important that there is minimal resistance so that the fluid in upper portion 40 can be quickly released to ensure a full flush occurs. Groove 53 provides a significantly sized space to receive fluid from passageway 13, which can then escape along drain channels 54.

In another preferred embodiment shown in figure 6, the venting insert and non-return valve support are shown manufactured as one piece called a "venting sleeve" 58. The sleeve is generally cylindrical such that its external surface approximates that of the internal surface of the non-return valve. It has a flange 55 to locate it within flange 46 of non-return valve 36 and a top flange 56 to locate it within the secondary recess in valve body 8 defined by wall 65 in place of venting insert 51 which is shown in figure 2. Apertures 57 (only one is shown in figure 6) replace drain channels 54 to permit fluid from the subsidiary passageway outlet 13a to enter the non-return valve. Accordingly, the venting sleeve 58 functions essentially the same way as the combination of the venting insert 51 and non-return valve support 49.

The whole assembly is then held firmly by flush pipe adaptor 47 (shown in perspective in figure 5), which is threadedly connected to valve body 8 and has an upper surface which acts on the lower surface of flange 46 such that, when it is screwed up tight against valve body 8, flange 46 is compressed between flush pipe adaptor 47 and valve body 8 to form the seal. As shown in figure 5, adaptor 47 has flats 39 to facilitate it being screwed tight against valve body 8. A washer 44 is located between the top of flush pipe adaptor 47 and flange 46. Nut 55 threadedly affixes to the external surface of flush pipe adaptor 47. Nut 55 has an internal flange or step of corresponding diameter to the lower surface of flush pipe adaptor 47. An "O"-ring 37 is located between this flange or step and the flush pipe adaptor to seal the flush pipe 48 upon tightening of nut 55. In one preferred embodiment, the flush pipe adaptor 47 has internal flanges 59 perpendicular to its axis in between slots 50 (as shown in figure 5). Figure 5 shows the flush pipe adaptor 47 with slots or apertures 50 which enable air to enter the top of flush pipe 48 as the top of flush pipe 48 abuts the internal flanges of adaptor 47. In use, the end of the flush pipe 48 rests on these flanges to locate it appropriately within the discharge chamber 14. However, where a flush pipe of larger diameter is required, this can be screwed on to the outside thread of nut 55 (in which case "O"-ring 37 is unnecessary).

The valve operates as follows. When the valve is in the closed position, the inlet chamber and main chamber 12 are filled with water. In this state, the total force exerted on the top of the piston 17 by the water contained in the upper portion 40 of the main chamber 12 is greater than the force exerted by the water in the lower portion of the main chamber 12 because the piston 17 has greater surface area exposed to the upper portion 40. In this state, the valve is closed because seal 18 prevents water flowing from the inlet chamber to discharge chamber 14. Upon actuation (by either mechanical or electrical means) of the control valve, water is permitted to flow from upper portion 40 through to passageway 13, to its end portion 13a, channel 53, channels 54 and then into non-return valve 36. Consequently, the force of the water on the top of piston 17 in the upper portion 40 of the main chamber becomes less than the force exerted by the water in the lower portion. This causes piston 17 to rise and permits water to flow from the inlet chamber through discharge chamber 14 and through the non-return valve 36. Water discharged from passageway 13 into non-return valve 36 is drawn (by a venturi effect by the water flowing from the inlet chamber to discharge chamber 14) down discharge chamber 14. In the open position, water from inlet chamber will still flow into channel 19, through filter 20, through flow valves 21 and 22 and then through channel 23 into upper portion 40. The non-return valve 36 provides some resistance to the water flowing through discharge chamber 14 which reduces any vacuum or venturi force created by the flowing of water through the outlet and which would otherwise cause piston 17, at normal operating pressures, to be prematurely drawn down, closing the valve prior to the action of the closing mechanism explained below. Further, where the non-return valve 36 is constructed of flexible and elastic material, it can provide an appropriate degree of resistance over the range of water flow-rates experienced in the discharge chamber 14 with a mains pressure inlet.

Upon release of the actuating means (which in normal use would be very shortly after actuation), water is no longer able to pass through from upper portion 40 through to passageway 13 as the control valve closes. Thus, water flowing through piston 17 into upper portion 40 will force piston 17 back down to its initial position in the "closed" state. As seal 18 nears its seat 18a in main body 8, the flow of water from inlet chamber to discharge chamber 14 will slowly decrease. Non-return valve 36 maintains some resistance to the water being discharged by elastically contracting due to the lower flow-rate (and thus lower pressure inside the non-return valve).

Projection 39, the choke, further slows the downward movement of the piston 12 by further decreasing the water flow-rate through discharge chamber 14 as piston 17 approaches the closed position. This assists in the seal 18 coming to rest on its corresponding seat 18a gently. A sudden or violent re-seating of piston 12 would cause an undesirable noise and may also set up dangerous or damaging hydraulic vibrations. The flow of water though the valve finally stops upon seal 18 again forming a seal with its corresponding seat 18a in main body 8 preventing the flow of water from the inlet chamber to discharge chamber 14.

It will be apparent from the preceding description that a valve as described above will seal better to reduce fluid leakage and more smoothly to minimise any water hammer. With the preferred embodiment of the invention, the volume of water delivered can be controlled over a range sufficiently broad for normal use with smooth operation and minimal leak.

The body and components of the valve may be manufactured from any material which has sufficient strength, resilience and non-corrosive properties to withstand the pressures involved (typically up to 2,000 Pa). Such materials include usual plumbing alloys, such as brass, but could also be stainless steel, and may also include high-strength polymers, including Nylon compounds. The seals are typical rubber "O-rings" and the non-return valve is also rubber as known in the art. Other advantages and modifications to the basic invention and its construction as described above will be apparent to those skilled in the art and all modifications and adaptations are included in the scope of the invention.

Claims

ClaimsThe invention is defined by the following claims.

1. A mains pressure flusher valve which includes: a valve body defining (i) a main chamber having a main inlet for fluid and a main outlet for fluid and (ii) a discharge chamber extending downstream from the main outlet, the discharge chamber being adapted to be connected in use to a flush pipe; a piston located in the main chamber which is moveable into and out of sealing engagement with the main outlet; a non-return valve located in the discharge chamber having a mouth at its upstream inlet and an outlet, the non-return valve being adapted to inhibit fluid flowing from the downstream side of the non-return valve to any part of the mains pressure flusher valve upstream of the non-return valve; sealing means to inhibit fluid in the discharge chamber from escaping, in use, to an external surface of the flush pipe; a subsidiary passageway having (i) a first portion with an entry for fluid in fluid communication with an upper portion of the main chamber above the piston, (ii) a control valve to permit flow of fluid through the subsidiary passageway and (iii) a downstream end portion adjacent to the discharge chamber with an outlet for fluid into the discharge chamber, the outlet for fluid located downstream of the main outlet and upstream of, and spaced from, the sealing means.

2. A valve according to claim 1 in which the valve body further wholly defines the end portion of the subsidiary passageway.

3. A valve according to claim 1 or 2 in which the sealing means includes an annular surface of the valve body around the discharge chamber normal to the direction of fluid flow, in use, through the valve body co-operating with a resilient flange on the non-return valve to form a seal.

4. A valve according to claim 3 in which the sealing means further includes a flush pipe adaptor which engages the valve body to hold the resilient flange against the valve body.

5. A valve according to any one of claims 1 to 4 in which the flush pipe adaptor further includes elongate apertures adapted to permit air to flow into the flush pipe, the apertures being located downstream of the non-return valve but, in use, located above the non-return valve outlet such that fluid downstream of the non- return valve is directed by gravity away from the apertures.

6. A valve according to any one of claims 1 to 5 in which the non-return valve is constructed of a resilient flexible material such that greater flow of fluid through the outlet causes the non-return valve to expand to permit a greater flow rate of fluid through the non-return valve.

7. A valve according to any one of claims 1 to 6 in which the piston has an internal passageway which communicates between an upper portion of the main chamber and the inlet and the non-return valve is adapted to provide resistance to fluid flowing therethrough to increase the pressure of fluid at the inlet of the internal passageway such that the non-return valve cooperates with the internal passageway to generate sufficient flow of fluid through the internal passageway during movement, in use, of the piston towards the main outlet to promote movement of the piston into a position of sealing engagement with the outlet.

8. A valve according to claim 7 further including at least one flow valve located in the internal passageway of the piston to regulate the passage of fluid through the internal passageway.

9. A valve according to any one of claims 1 to 8 in which the piston further includes a depending projection of smaller diameter than the main outlet adapted to promote smooth movement of the piston into sealing engagement with the outlet.

10. A valve according to any one of claims 1 to 9 further including mechanical and/or electrical actuation means to actuate the control valve.

11. A mains pressure valve according to any one of claims 1 to 10 further including a venting insert (as herein defined) in the discharge chamber, the venting insert including: an inlet located downstream of the main outlet and upstream of the subsidiary passageway outlet and adapted such that at least substantially all of fluid flowing, in use, through the main outlet flows through the venting insert inlet; an outlet downstream of the subsidiary passageway outlet; and an exterior cavity in the external surface of the venting insert adapted to form at least one channel for fluid from the subsidiary passageway outlet to the venting insert outlet.

12. A valve according to claim 1 1 in which the exterior cavity includes a circumferential groove in an exterior surface of the venting insert, the groove being substantially aligned in situ with the subsidiary passageway outlet, and the cavity also including at least one channel leading from the circumferential groove to the venting insert outlet.

13. A valve according to any one of claims 1 1 or 12 in which the venting insert inlet is accommodated within an annular recess within the valve body adjacent the main outlet.

14. A valve according to any one of claims 1 to 13 further including a rigid non-return valve support located within the non-return valve and adapted to support the non- return valve in situ in the valve, the valve support having an upstream mouth adjacent to and inside the mouth of the non-return valve, the valve support's mouth being adapted to co-operate with the venting insert outlet such that fluid from the main outlet and the subsidiary passageway outlet is directed into the non-return valve.

15. A valve according to claim 13 in which the valve support and venting insert are one piece.

16. A valve according to any one of claims I to 15 further including piston stop means located in the upper portion of the main chamber and opposite the piston, the piston stop means being adapted to form a stop to movement of the piston, in use, away from the outlet and such that the piston stop means does not obstruct or enter the internal passageway.

17. A valve according to claim 16 in which the piston stop means is adjustable to control the amount of movement away from the outlet of the piston in the main chamber.