WO1995000784A1

WO1995000784A1 - Reduced pressure zone backflow prevention valve

Info

Publication number: WO1995000784A1
Application number: PCT/AU1994/000345
Authority: WO
Inventors: Lloyd Joseph Dixon
Original assignee: Valvtec Pty. Ltd.
Priority date: 1993-06-23
Filing date: 1994-06-23
Publication date: 1995-01-05

Abstract

A valve assembly (10, 10A) including a valve body (11) having a reduced pressure zone (53) within an interior thereof (11A) and a drain port (54) which may communicate with the reduced pressure zone (53), said valve body (11) having an inlet (12, 12A) and an outlet (13, 13A), a piston member (19) movable in the valve body (11) from a first position allowing fluid flow through the valve body interior (11A) to a second position which allows fluid flow through the drain port (54), an upstream check valve (27) including a movable valve member (28) and associated valve seat (29), a downstream check valve (44) including a movable valve member (45) and associated valve seat (50), a single biasing means (31A) associated with the upstream check valve (27) and also the piston member (19) and operable to move the movable valve member (28) of the upstream check valve (27) to seal its associated valve seat (29) and also to move the piston member (19) to the second position to enable fluid trapped in said valve body interior (11A) downstream of the upstream check valve (27) to move out of the valve body (11) through the drain port (54).

Description

TITLE REDUCEDPRESSUREZONEBACKFLOWPREVENTIONVALVE

FIELD OF INVENTION THIS INVENTION relates to an improved valve assembly especially adapted for use as a reduced pressure zone backflow preventer for water supply mains to prevent backflow and siphonage of water in the event of mains pressure decrease or failure. However it will be appreciated that valve assemblies constructed in accordance with the invention may be used generally.

BACKGROUND ART Backflow preventers are now required by many municipal authorities to prevent the possibility of contamination of the mains by backflow in the event of mains pressure failure from end users such as hairdressers, medical services, veterinary services and laboratory services as well as factories producing pesticides and other toxic chemicals. The relevant standard which is applied to backflow preventers specifies that two independent check valves be installed and that the space between the check valves be drainable. This arrangement ensures that a reduced pressure zone is obtained between the check valves which vents to atmosphere upon mains pressure failure.

Reference may be made to PCT specification

AU/89/00219 published under WO 89/11611 which describes a typical valve assembly for use as a backflow preventer. This specification describes a valve assembly having a valve body, an inlet end cap and an outlet end cap. The interior of the valve body is provided with a piston and associated downstream seat which divides the valve body into an upstream chamber and a downstream chamber. The downstream chamber is provided with a check valve and associated check valve spring as well as an associated seal permitting flow in a downstream direction only. The piston is provided with an axial passage therethrough which passage is provided with a non return valve also having a non return valve spring permitting only downstream flow. In use mains water pressure maintains the piston in sealing contact with the downstream seat against the force of an outer spring surrounding the piston spring. There is provided a reduced pressure zone between the check valve and the non return valve by the differential loading between the non return valve spring and the outer spring. In the event of the mains pressure falling below a specified level both the check valve and non return valve close to prevent back flow or siphonage. The piston is also caused to abut an upstream seat located in the inlet end cap and is thus urged away from the downstream seat by the spring which is biased toward the upstream seat. This has the result off the reduced pressure zone opening to atmospheric pressure and thus any contaminated water which has passed through the check valve on failure of the mains pressure will drain from the reduced pressure zone through a drain port in the valve body.

Reference is also made to US Patent 3 818 929 which also describes a reduced pressure backflow preventer valve which has a valve body with a vent chamber, the inner end of which forms a relief valve seat. This valve seat is engaged by the base of a cup member to close off the vent chamber. The cup member is supported on an inner edge of an annular flexible diaphragm with an outer edge secured to the valve body. The cup member has an internal check valve seat and contains a check valve biased against the check valve seat.

Problems associated with the abovementioned prior art include the fact that often difficulty was experienced in maintaining the desired reduced pressure zone in the valve body. Thus for example in specification PCT/AU89/00219 the spring loading of the non return valve spring which was greater than the outer spring provided a relatively difficult procedure for achieving the desired reduced pressure zone because of the necessity of calibrating and testing each spring. Also the use of three springs in the valve body meant that manufacture was expensive and increased costs of the relevant tooling. Also use of these springs meant increased hydraulic pressure losses or decreased flow rate from inlet to outlet. This meant that a valve assembly constructed in accordance with patent specification PCT/AU89/00219 did not meet with required Australian standard AS2845 flow rates and losses. In regard to US Specification 3,818,929 difficulties would be experienced because of the use of three springs for the reasons already described above with specification PCT/AU89/00219. Also another major problem was the use of a diaphragm which often would not provide the correct alignment for sealing between the valve and the valve seat.

Reference may also be made to US Specifications 4,506,694; 3,346,001; 3,283,772; 3,850,190; 3,171,423 and 4,552,177 as well as Specification EP 0002600. These are not believed to be relevant to the present invention. Reference also may be made to German Specification 2424978, US Specification 3,083,723; German Specification 2418822; German Specification 2414893; PCT/US86/02143 and US Specification 4013089 which is a modification of US Specification 3818929 described above which are also not believed to be relevant to the present invention.

SUMMARY OF THE INVENTION It therefore is an object of the invention to provide a valve assembly suitable for use as a reduced pressure zone backflow prevention which may alleviate the abovementioned disadvantages associated with the prior art.

The valve assembly of the invention includes:

(i) a valve body having a reduced pressure zone within an interior thereof and a drain port which may communicate with the reduced pressure zone, said valve body having an inlet and an outlet;

(ii) a piston member movable in the valve body from a first position allowing fluid flow through the valve body interior to a second position which allows fluid flow through the drain port; (iii) an upstream check valve including a movable valve member and associated valve seat; (iv) a downstream check valve including a movable valve member and associated valve seat;

(v) a single biasing means associated with the upstream check valve and also the piston member and operable to move the movable valve member of the upstream check valve to seal its associated valve seat and also to move the piston member to the second position to enable fluid trapped in said valve body interior downstream of the upstream check valve to move out of the valve body through the drain port. The valve body may be of any suitable shape and suitably includes an inlet aperture or passage, an outlet aperture or passage and an interior accommodating the piston member, the upstream check valve and the downstream check valve as well as the biasing means.

The valve body is suitably substantially cylindrical although any suitable shape may be adopted e.g. frusto conical for example. The valve interior may form a valve chamber of any suitable shape which also may conform to a cylinder interior. The valve body may also be connected to a mains pressure line in any suitable manner such as by an external thread or internal thread. The valve body may also be connected to an end user supply line also by a suitable manner such as by external thread or internal thread. The fluid port is suitably located in a continuous side wall of the valve body intermediate the inlet and the outlet.

The piston member may comprise a piston head suitably having one or more seals associated therewith and a piston body integral with or otherwise secured to the piston head in any suitable manner. Preferably the piston body includes flow passages and more suitably includes a plurality of ribs with veins or flow passages located between adjacent ribs. The piston member may also include an abutment part which abuts against an associated piston seat when required to permit fluid flow through the valve body from inlet to outlet. The upstream check valve includes a valve member of any appropriate shape and thus may comprise a cup shaped or hemispherical member or alternatively a ball or sphere if desired wherein the ball or sphere has an internal recess. The valve member may also include a valve stem projecting outwardly from the recess.

There also may be included a stationary mounting member fixedly located in the valve body interior which includes an outwardly projecting upstream end part having a valve stem retaining passage. The mounting member may also include another downstream end part located adjacent to an internal surface of the valve interior. The mounting member may also include a plurality of flow passages and in one form this may include a plurality of ribs interconnecting both end parts with veins or flow passages provided between adjacent ribs. Suitably the downstream end part is of greater diameter or transverse dimension when compared to the upstream end part. It is preferred that the stationary mounting member be integral although it will be appreciated that it can be formed from a number of mating components attached in any suitable manner.

In a variation of the foregoing the valve member of the upstream check valve may be provided with a stem retaining passage which engages with an outwardly extending stem of the stationary mounting member. However the former arrangement is preferred.

The downstream check valve may be of any suitable design and thus may include a valve member which may comprise a poppet or ball or any other suitable shape. The valve seat may also be of any appropriate form. Preferably however the valve member is of a similar shape to the upstream valve member and thus include an outwardly extending valve stem which may be received in a mating passage located in an outlet flow cap of the valve body. BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be made to a preferred embodiment of the invention as described in the following drawings wherein:

FIG 1 is a sectional view of a valve assembly constructed in accordance with the invention showing the piston member closed and both the downstream check valve and upstream check valve also closed;

FIG 2 is a similar view to FIG 1 showing the piston member closed but both the upstream check valve and the downstream check valve open to permit fluid flow through the valve body from inlet to outlet;

FIG 3 is a view similar to FIG 1 showing the upstream check valve closed and the downstream check valve open permitting back flow of liquid which may exit through the drain post from the reduced pressure zone after passing through an opening created by the piston member moving away from its associated piston seat; and

FIG 4 is a sectional view of a valve assembly constructed in accordance with the invention which is suitable for in line servicing or maintenance. DETAILED DESCRIPTION

The valve assembly 10 shown in the drawings includes valve body 11 having an inlet 12 and outlet 13. Valve body 11 has an interior or valve chamber 11A which accommodates the various valve components described hereinafter. Inlet 12 comprises an internally screw threaded passage 14 which may be attached to a mating screw threaded passage of a mains supply line (not shown). However it will be appreciated in a variation of this arrangement that an external thread may be provided at 15. In similar manner outlet 13 comprises an internally screw threaded passage 16 which may be attached to a mating screw threaded passage of an end user supply line (not shown). However if desired an external thread may be provided at 17. There are also provided ports 18 of valve body 11 which may be used for testing of the pressure of liquid flowing through valve body 11 at appropriate locations.

There is also shown piston member 19 which may include piston head 20, seal 21, piston body 22 connected to piston head 20 at 23, veins 24, ribs 25 and abutment part 26.

There is also shown upstream check valve 27 including valve member 28 and associated valve seat 29 comprising seat 29B and associated retaining member 29A. There is also included valve stem 30 and stationary mounting member 31 for coil spring 31A. Valve member 28 also includes seat 28A for spring 31A. Stationary mounting member 31 also has mating guide passage 32 located in upstream end projection 33 for valve stem 30, veins 34 located between ribs 35 and end part 36 located adjacent internal surface 37 of valve body interior 11A. Also shown are seals 38 and 39. Also provided is annular support body 40 with retaining member 41 and associated seal 42 which abut against abutment part 26 of piston 19. There is also provided passageways 26A located in end part 26B of annular support body 40.

The abutment part 26 of piston 19 seals against elastomeric piston seat 43.

The downstream check valve 44 includes valve member 45, valve stem 46, spring 47, mounting seat 48 for spring 47 and mating passage 49 for valve stem 46, and valve seat 50 comprising co-operating seals 51 and 52.

There is also shown outlet end cap 51 screw threadably attached to valve body 11 at 52A.

The reduced pressure zone 53 is also shown which communicates with drain port 54 when the piston member 19 is in an open position allowing fluid from outlet 13 to flow into the interior of the valve body 11 through the downstream check valve 44 as shown in FIG 3.

In operation of the valve assembly 10 of the invention FIG 1 shows a situation where both upstream check valve 27 and downstream check valve 44 are closed and piston member 19 is closed as described above.

The normal operative position is shown in FIG 2 when both check valves 27 and 44 are open as shown allowing water to flow through the interior of the valve body 11 as indicated by the arrows. The piston member 19 is closed as in FIG 1 and thus the reduced pressure zone 53 is isolated from drain port 54. The reduced pressure zone 53 is formed as a result of the spring 31A which has a pressure loading which is less than the mains pressure thus enabling the liquid to flow through check valve 27 with valve member 28 lifted away from mating valve seat 29 as shown in FIG 2. The flow of liquid also causes check valve 44 to open with valve member 45 lifted away from its mating valve seat 50 as also shown in FIG 2.

In FIG 3 when a situation occurs when mains .pressure falls below a specified level both check valves 27 and 44 close to prevent backflow of liquid or siphonage from the end user line through outlet 13. The piston member 19 is moved away from its mating seat 43 by the spring 31A causing check valve 27 to close wherein the reduced pressure zone 53 is opened to ambient pressure by communicating with drain port 54. Any possibly contaminated water which may have passed through check valve 44 (e.g. by an obstruction preventing closure of check valve 44) may drain from the reduced pressure zone 53 through drain port 54 as shown by the arrows in FIG 3 whereby passageways 26A are open to water flow by abutment part 26 lifting off valve seat 43 by movement of piston 19 towards an open piston. However it is emphasised that in normal operation the downstream check valve will be closed as indicated by the lines in phantom in FIG 3. The downstream check valve will be open only under rare circumsrtances ie. when the valve seat 50 is worn or an obstruction such as gut, sand or other foreign material is wedged in the valve seat 50.

The modified valve assembly 10A shown in FIG 4 is suitable for in line servicing or maintenance wherein strainer 19A and all internal components may be removed from valve chamber 11A by removal of outlet 13A through rotation of 180° by appropriate means (not shown) normal to the plane of the drawing after removal of end cap 17 and thus providing access to valve chamber 11A. If desired inlet 12A may also be rotated normal to the plane of the drawing after removal of end cap 15 and thus provide access to strainer 19A. Alternatively strainer 19A may be removed from valve body 11 by removal of end cap 15. End cap 15 is screw threadedly attached to valve body 11 at 15A. There is also provided a head part 20A attached to valve member 28 by screw fastener 20B. Valve member 45 also is provided with removable head part 45A attached to valve member 45 by fastener 45B. The purpose of each head part 20A and 45A is to retain the U shaped seals comprising valve seats 29 and 50 in desired position. There is also provided insert sleeve 40 having a tapered edge which constitutes seat 43 for piston 19. There is also provided U shaped seal 23A.

The valve assembly 10A is otherwise provided with the same or similar components as shown in FIGS 1-3 and thus the same reference numerals have been utilised for this purpose.

The advantage of the valve assembly of the invention in contrast to the abovementioned prior art as illustrated in the preferred embodiment described above is that the construction of the valve assembly is much simpler than that described in Specification PCT/AU89/00219 because only two springs are used instead of three and in particular a single spring is used to control movement of the upstream check valve and also the piston member. This provides additional advantages in that it enables the valve assembly of the invention to achieve much higher flow rates than the prior art valve assembly described in Specification PCT/AU89/00219. Thus, for example, valve assemblies constructed in accordance with PCT/AU89/00219 did not pass Australian standard 2845.1-90/91 rated water flow capacity and pressure loss for reduced pressure zone devices Table 11.2. However valves assemblies constructed in accordance with the present invention have passed this standard. Thus for example having regard to a mains pressure of 500 kPa the downstream end of the valve for a flow of 1.9 litres per second should give a minimum of 360 kPa downstream in the end user line. Valve assemblies constructed in accordance with the present invention provide a downstream pressure of 435 kPa with reference to the same flow rate. Valve assemblies constructed in accordance with PCT/AU89/00219 will only provide a downstream pressure of 325 kPa.

The provision also of the piston member and the stationary spring mounting member having flow passages also results in less restricted water flow through the valve body interior which also facilitates the higher flow rates described above.

Claims

CLAIMS :

1. A valve assembly including -

(v) a single biasing means associated with the upstream check valve and also the piston member and operable to move the movable valve member of the upstream check valve to seal its associated valve seat and also to move the piston member to the second position to enable fluid trapped in said valve body interior downstream of the upstream check valve to move out of the valve body through the drain port.

2. A valve assembly as claimed in claim 1 wherein the piston body includes flow passages which provide fluid communication between the inlet and the valve body interior downstream of the upstream check valve when the upstream check valve is open.

3. A valve assembly as claimed in claim 1 wherein the piston body includes an abutment part which abuts against an associated piston seat to permit fluid flow through the valve body interior from inlet to outlet when the upstream check valve and the downstream check valve are in an open position.

4. A valve assembly as claimed in claim 1 wherein the valve member of the upstream check valve includes a head part having an outer surface which is arcuate.

5. A valve assembly as claimed in claim 1 wherein the valve member has a valve stem surrounded by a spring constituting said biasing means.

6. A valve assembly as claimed in claim 5 wherein the valve member includes an upstream end seat for said spring.

7. A valve assembly as claimed in claim 1 wherein the valve member of the downstream check valve includes a head part having an outer surface which is arcuate.

8. A valve assembly as claimed in claim 7 wherein the valve member includes an arcuate head portion and a depending valve stem with downstream biasing means surrounding said valve stem.

9. A valve assembly as claimed in claim 5 including a stationary mounting member in the valve body interior having a retaining passage for the valve stem.

10. A valve assembly as claimed in claim 9 wherein the stationary mounting member also includes a downstream end seat for said spring.

11. A valve assembly as claimed in claim 9 wherein the stationary mounting member also includes one or more flow passages thereby establishing fluid communication between the valve body interior downstream of the upstream check valve and the valve body outlet when the downstream check valve is open.

12. A valve assembly as claimed in claim 1 wherein the reduced pressure zone is formed as a result of the single biasing means having a pressure loading which is less than mains pressure.

13. A valve assembly as claimed in claim 1 suitable for inline servicing or maintenance wherein internal components included in the valve body interior may be removed by rotation of said valve body inlet or outlet after removal of an adjacent end cap.

14. A valve assembly as claimed in claim 13 further including a strainer in the valve body interior.