AU9514401A - Backflow preventer - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): TYCO FLOW CONTROL PACIFIC PTY LTD A.C.N. 000 922 690 Invention Title: BACKFLOW PREVENTER a The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 BACKFLOW PREVENTER This invention relates to a backflow preventer or device in the form of a specialised non-return valve which 15 can be incorporated in a pipeline for potable water supply in a domestic, commercial and/or industrial installation.

The purpose of the device is to prevent unintentional reversal of water flow (backflow) in circumstances where downstream pressure within the supply exceeds upstream 20 pressure whereby the reversal of flow of water back to main supply may possibly contaminate the main water supply.

Backflow can also occur through the phenomenon of back-siphonage. This is the case when there is negative 25 water pressure generated in the supply mains. An example of back-siphonage is if a water authorities water mains pipe has burst open at a level below the outlet in question, causing all water with in the system to flow towards the break, generating negative pressure in the line.

Backflow preventers have to meet various standards set by International Authorities in terms of how they are to perform as well as the materials from which they are manufactured. The standards relate to various environment or hazard situations that are rated accordingly to the severity of risk if backflow was to occur, and the H:\Leanne\Keep\prov.gm30231.doc 28/11/01 3 present invention has been developed specifically for so called "reduced pressure zone" (RPZ) for high hazard situations and so called "double check valve" (DCV) for medium hazard situations.

A typical backflow preventer has an inlet chamber communicating with an inlet port, and an outlet chamber communicating with an outlet port, and with two longitudinally spaced apart non-return valves, one, (a first non-return valve) adjacent the inlet chamber and another (a second non-return valve) adjacent the outlet chamber and defining therebetween an intermediate chamber.

When upstream pressure is at a required pressure, water pressure within the inlet chamber forces the first nonreturn valve to open, and as water pressure builds within S the intermediate chamber the second non-return valve is forced to open and water flows into the outlet chamber and out through the outlet port. When downstream pressure, for some reason, exceeds upstream pressure, the downstream 20 pressure acts to close the second and first non-return valves in succession preventing water backflow, whilst a relief port communicating with the intermediate chamber vents any contaminated water to the outside of the device.

25 Conventional backflow preventers or devices are manufactured from cast components which are firstly complicated to cast and secondly difficult to machine. The main body of the preventer is of an elongate cylindrical configuration and its ends are closed by end caps fastened to the ends of the main body by various forms of threaded fasteners. Such conventional backflow preventers are, as a consequence, costly to manufacture and as a further consequence the cost to the user is unnecessarily high.

One proposal in the past to reduce manufacturing costs has been to use a thick walled stainless steel pipe for the main body whilst its ends are closed by end caps H:\Leanne\Keep\prov.gm30231 .doc 28/11/01 4 attached by threaded connections or clamping mechanisms.

The first non-return valve is mounted within a piston assembly. When the inlet pressure reaches a minimum of the piston will be forced across a relief vent and seal water-tight on a relief seat. The first non-return valve will remain closed until the pressure increases further to 65kPa. When forced open with the increase of pressure, the first non-return valve allows water to pass through the piston and relief seat and onto the second nonreturn valve. The second non-return valve, which acts independently of the first non-return and piston, is situated directly downstream of the relief seat. When the :i pressure in the piston (intermediate chamber) increases by a further minimum of 7kPa the second non-return valve will begin to open and allow flow through to the outlet chamber.

Under the conditions of the back pressure and back-siphonage, both non-return valves will close simultaneously and the piston will open under spring pressure to relieve the water contained in the intermediate chamber to atmosphere. In that situation there is a physical air gap between the two non-return valves within •the valve housing.

*"25 However, this design also did not meet S"international standards and was also expensive to manufacture, whilst servicing was not easy and the manner of venting the intermediate chamber did not comply with international standards.

It is therefore an object of the present invention to provide a backflow preventer or device which eliminates, or at least minimises, the above problems.

In accordance with the invention, there is provided a backflow preventer or device for a water supply system, said device including an elongate thin walled H: \Leanne\Keep\prov.gm30231 .doc 28/11/01 5 housing having inlet and outlet ports at, or adjacent, the ends of said housing, end closures at either end of said housing, and a pair of longitudinally spaced apart first and second non-return valves within said housing, said first non-return valve being in communication with said inlet port via an inlet chamber within said housing and said second non-return valve being in communication with said outlet port via an outlet chamber within said housing, with the space between said non-return valves defining an intermediate chamber within said housing, said non-return valves being adapted to close in response to downstream pressure exceeding upstream pressure under backflow conditions, a pressure relief valve support carried by said non-return valves, and extending through the intermediate chamber and having passage means communicating with said inlet chamber, said pressure relief valve support carrying a pressure relief valve adapted to close a pressure relief port through the wall of said housing in response to pressure within said inlet chamber and via said passage 20 through said pressure relief valve support but adapted to open said relief port to relieve water pressure in, and flush, said intermediate chamber between the non-return valves under backflow conditions when pressure in said inlet chamber drops below a predetermined value, wherein at *.25 least one tie rod is provided connected to each of said end closures to hold said end closures in their positions closing the ends of said housing, said tie rod or rods extending along the length of the interior of the housing and through, and attached to and thereby locating, said non-return valves.

One preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which; Figure 1 is a longitudinal cross-sectional view of the backflow preventer or device of this preferred H:\Leanne\Keep\prov.gm30231 .doc 28/11/01 6 embodiment of the invention, and Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1.

Turning to the drawings, the backflow preventer or device, generally indicated as 10, includes an elongate cylindrical thin walled housing 11 preferably of stainless steel, and having an inlet port 12 through the wall of the housing, and adjacent one end, and an outlet port 13 also through the wall of the housing, and adjacent the other end. Each end of the housing is closed by shallow cupshaped closure members 14 with radially inwardly spaced annular flanges 14a received within the interior of the 15 ends of the housing and having 0-rings 15a in grooves with the O-rings sealing with the interior of the housing.

A pair of longitudinally spaced apart non-return valves 16 are positioned within said housing on either side of the mid-point of the length of the housing to in effect define an inlet chamber 17 with which the inlet port 12 oooo communicates; an intermediate chamber 18 (between the two non-return valves); and an outlet chamber 19 with which the outlet port 13 communicates.

Each non-return valve 16 includes a disk-shaped valve body 16a with an annular valve port 16b therethrough defined by an outer peripheral wall 16c of the main body and a central valve support and guide member 16d connected by one or more spoke members 16e to the outer peripheral wall 16c of the main valve body. A water seal between the periphery of the valve body and the interior of the wall of the housing is provided by an O-ring 16f located in a groove around the periphery of the valve body. A valve member 16g is provided for each non-return valve and has a head 16k the underside 16i of which carries an annular disc shaped washer 16m which seats against an annular seat 16j H:\Leanne\Keep\prov.gm30231 .doc 28/11/01 7 on the downstream side of the valve body and around the valve port 16b, and consisting of an axially directed annular protrusion 16n on the radially inner side of the outer peripheral wall 16c. The head 16k is carried by a valve stem 16k' which extends through a guide bore 16e through the guide member 16d, whilst the extreme end of the valve stem has a flange 16q. A compression coil spring 16p is captured between a washer 16r, bearing against the flange 16n, and the facing end of the guide member 16d and serves to normally bias the washer 16m on the underside 16i of the head 16k into engagement with the seat 16j.

A pressure relief valve 20 is carried by a °.pressure relief valve support member 21 connected to, and 15 bridging the space between, the non-return valves, that is, through the intermediate chamber 18. The pressure relief valve support member 21 has a passage 22 therethrough communicating the inlet chamber 17 with a relief valve chamber 23 adjacent which is received a relief valve member 20 24 which under water pressure in the inlet chamber 17, and against the bias of a compression coil spring 25 seats around to close a pressure relief port 26 through the wall 00 of the housing. Such provides water pressure relief through the port 26 by virtue of water pressure in the inlet chamber 17, via the passage 22 and chamber 23 and thereafter and against the relief valve member to move it to a position closing the port 26. The relief valve member 24 is guided by a combination of cylindrical central sleeve 27 forming part of integral cup-shaped member 28 forming part of the valve support member 21. The coil spring 25 is captured between the inner end 31a of a cup-shaped flexible sealing member 31 and the head 32 of a guide pin 33 extending through the coil spring 25 with its end located in a blind hole 34a formed in an axially aligned protrusion 34 also forming part of the valve support member 21. The spring 25 serves to guide the relief valve member into and out of engagement with the port 26 under the prevailing H:\Leanne\Keep\prov.gm30231 .doc 28/11/01 8 water pressure conditions within the backflow preventer or device whilst at the same time biasing the valve member away from the relief port under backflow conditions. The outer periphery of the relief valve member 24 is also on guided during its axial movement by a cylindrical passage with the valve support member 21, whilst sealing "O" rings 34 and 35 in associated grooves are provided between the valve member 24 and cylindrical passage 30, and between the cup-shaped member 28 and the interior of the valve member 24, respectively. A radially outwardly directed flange 31b on the cup-shaped flexible sealing member 31 acts the seal the valve member 24 against the inside of the housing 11 around and outside the periphery of the pressure 1 relief port 26.

i The main bodies of the non-return valves 16 are identical, and as a consequence the structures of the nonreturn valves are also identical, and the main bodies thereof have identical recesses 16z formed in their downstream sides. The recess 16z in the main body of the first non-return valve receives one end 21a of the pressure relief valve support 22 at the first non-return valve together with intervening ring seal 21b, whilst the other end of the pressure relief valve support 21 has a 0 0.

threaded extension 21c extending through the main body of the second non-return valve and into its recess 16z, and a nut 21d is screwed onto the extension 21c to connect that end of the pressure relief valve support to the main body of the second non-return valve. As the non-return valves 16 are identical, particularly their main bodies 16a, only one form of non-return valve constructions needs to manufactured and performs the function required for either the first or second non-return valves without two different valve constructions being necessary.

In accordance with the present invention, the backflow preventer or device further includes, in this Leanne\Keep\prov. gm30231.doc 28/11/01 9 preferred embodiment, tie rods 36 coupled by bolted connections 37 to the respective end closure members 14 and which when tightened draw the end closure members 14 into tight sealing engagement within the respective open ends of the cylindrical thin walled housing. The tie rods in turn extend through, and are attached to, the valve bodies 16a of the non-return valves 16 to locate them in position and also to locate the pressure relief valve 20 in position aligned with its associated relief port 26.

During operation, when water flows through the device in the required direction, water pressure within the inlet chamber 17 acts to open the non-return valve adjacent :i that chamber, as dictated by a predetermined spring force 15 of its compression coil spring and water pressure builds up in the intermediate chamber 18. At the same time, water pressure in the inlet chamber 17 is exerted, via passage 22 and chamber 23 within the pressure relief valve support member 21, against the pressure relief valve member 24 to S 20 maintain it in a position closing the pressure relief port 26, as distinct from the position spaced from and opening the port as shown in the drawings. As water pressure increases within the intermediate chamber, and once again dictated by a predetermined spring force of its compression 00 25 spring, the second downstream non-return 16 valve opens.

As a consequence water flow through the backflow preventer or device is achieved.

When downstream water pressure exceeds upstream water pressure due to a drop in upstream water pressure, the downstream pressure acts to close the downstream nonreturn valve and thereafter the upstream non-return valve, whilst at the same time the reduction of water pressure in the inlet chamber, and via the passage 22 and chamber within the valve support member, relieves water pressure on the pressure relief valve member 24 and it moves away from the pressure relief port 26, to a position as shown in the H:\Leanne\Keep\prov.gm30231.doc 28/11/01 10 drawings, and allows relief of the water pressure within the intermediate chamber. When the inlet water pressure again increases to an acceptable value, the non-return valves open and the pressure relief valve closes and the backflow preventer or device operates as normal.

In accordance with conventional practice, test cocks 40 may be provided for the inlet, intermediate and/or outlet chambers, to monitor water pressure in the relevant chambers.

e* H:\Leanne\Keep\prov.gm30231 .doc 28/11/01

Claims (3)

1. 2. A backflow preventer or device as claimed in Claim 1, wherein each said non-return valve has a main body with a valve port therethrough and a valve member spring biased to close its respective valve port in response to said downstream pressure exceeding said upstream pressure, and wherein said pressure relief valve support is connected between the main body of the respective non-return valves. 15 3. A backflow preventer or device as claimed in Claim 2, wherein said main bodies of said non- return valves are identical and have identical recesses formed in their downstream sides, said 0oo*** recess in the main body of said first non-return valve receiving one end of said pressure relief valve support at said first non-return valve, ooooo whilst the other end of said pressure relief Ooooo valve support having means extending through the main body of said second non-return valve and o .°25 into its recess with means in said recess to connect said pressure relief valve support to said main body of said second non-return valve.
2. 4. A backflow preventer or device as claimed in any one of the preceding claims, wherein said end closures have radially inwardly flanges extending axially of said housing, and within the ends thereof, and said the or each tie rod has threaded extensions at each end thereof and extending through the respective end closures to receive nuts which when tightened draw the end closures into tight sealing engagement within H:\Leanne\Keep\prov.gm30231.doc 28/11/01 13 their respective ends of said housing. A backflow preventer or device as claimed in any one of the preceding claims, wherein said pressure relief valve is held in a position closing said pressure relief port under water pressure during normal pressure conditions in said inlet chamber and against the spring bias of a compression spring between said pressure relief valve and said pressure relief valve support and which serves to move said pressure relief valve away from said pressure relief port to open said port during backflow conditions and whereby to relieve water pressure within, and flush, said 15 intermediate chamber.
3. 6. A backflow preventer or device, substantially as hereinbefore described with reference to the accompanying drawings. Dated this 28th day of November 2001 TYCO FLOW CONTROL PACIFIC PTY LTD By their Patent Attorneys 25 GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia H:\Leanne\eep\prov.gm3023I.doc 28/11/01