BACKFLOW PREVENTION VALVE

Abstract: A backflow prevention valve having a hollow housing (1) having an inlet check valve (5) and an outlet check valve (16) for fluids flowing through the housing and having a drain (4) from the housing with a drain valve (10) coupled to the inlet check valve (5) to open the drain valve (10) when the inlet check valve (5) is positioned to close the inlet (2) and optionally an atmospheric vent valve (9) to the hollow of the housing.

Description: BACKFLOW PREVENTION VALVE This invention relates to a backflow prevention valve for pressure fluids and in particular it relates to a valve adapted to be inserted between a pressure fluid supply and a consumer area. A problem with, for instance, domestic supplies or supplies to industrial areas is that, should a backflow occur in a mains fluid supply, such as a water supply, contamination will take place of the supply source by backflow from the consumer area. Such a condition is highly undesirable and while for instance it is possible to have a non-return valve in a pressure supply line, such valves are not in themselves acceptable because, in the event of a leak or malfunction, backflow can take place when the supply pressure drops below that of the consumer area. To overcome this problem, valves have been proposed in which, as well as using a nonreturn valve, an air admission valve is included which breaks backflow should the nonreturn valve fail, such a valve being shown for instance in the specification of U.K. Patent GB 218181 9A of Bjorn Andersson in which a chamber is used between the pressure source and the consumer area, and in the chamber is positioned a valve arranged to allow air to flow into the chamber to prevent flow from the fouled consumer area to the pressure source. A similar assembly is shown in U.S. Patent No 3,951,164 of Buckiey Crist which uses a pair of disc valves in a chamber, one to act as a backflow preventor, the other to bleed air units into the system to prevent flow to a fouled pressure source from the fouled consumer area. It is an object of this invention to provide a form of valve, which although it is connected between a pressure source and a consumer source, has improved safety factors, in that where the fouled consumer area backflow is above atmospheric pressure and pressure source pressure no fouling of the pressure source area occurs. This is achieved according to this invention by so arranging valve means that outflow from a drain valve to the atmosphere occurs when the pressure in the consumer source exceeds that in the supply source or when both pressures are equal but less than atmospheric at both points, and preferably the chamber is connected to the atmosphere when the pressure of the pressure source falls below the pressure at the consumer area. The mechanism of the invention is such that if a malfunction occurs and the pressure at the consumer area is higher than the pressure at the pressure source, or either or both pressures are less than atmospheric, an outlet valve closes but at the same time a drain valve opens to cause outflow from the valve. to the atmosphere, while the inlet valve also closes and according to a preferred form an atmospheric vent valve opens to place a chamber in a housing which is disposed between a fluid inlet to the valve and the fluid outlet therefrom to be maintained at atmospheric pressure. Basically the backflow prevention valve of this invention comprises a housing having a chamber therein and having an inlet for fluid thereinto and an outlet for fluid therefrom and including at least a check valve in the inlet to prevent backflow through the inlet, characterised by a drain in the housing to drain fluid from the chamber in the housing, and by a drain valve in the housing to control flow through the drain, the check valve in the inlet being coupled to the drain valve to open the drain when the inlet check valve in the inlet is closed. The backflow prevention valve can be constructed in various ways but preferably comprises a housing which has at one end an inlet for the fluid and in the inlet a non-return check valve movable to allow flow into the chamber under normal pressure conditions, the outlet allowing flow to the consumer device, but this inlet valve is coupled to a drain valve by a special arrangement which closes the drain valve when the inlet valve is open but to open the drain valve when the inlet valve is closed, the coupling preferably using both mechanical means and fluid pressure contact to effect the control to ensure that backflow is prevented. In the preferred form the invention also relates to the use of a check valve in the outlet and to an atmospheric vent valve in the housing to vent the chamber in the housing to allow air flow into the chamber when the drain valve is open to drain fluid from the chamber of the housing. The method of the invention comprises bypassing the fluid from the chamber of the housing to atmosphere through the drain valve when flow through the chamber is toward the inlet, and optionally admitting air into the chamber through air atmospheric vent valve during such flow. To enable the actual construction of the invention to be better appreciated, an embodiment of the invention will now be described with reference to the accompanying drawing in which: FIG. 1 is a longitudinal section of such a valve, FIGS. 2 and 3 show respectively at a reduced scale the main valve components in a exploded view and in plan, FIGS 4, 5, 6 and 7 show schematically the functional positions of the valves under selected conditions, FIG. 4 showing the valve in a static condition with the various valves in their spring loaded locations, FIG. 5 showing the valve positions in a normal flow arrangement, FIG. 6 showing the back pressure position, and FIG. 7 indicating how atmospheric air is admitted to the chamber. The valve comprises a housing 1 defining with a closure cap 1a a chamber which has at a first end, an inlet 2 for fluids, and at a second end an outlet 3 for fluids and a drain 4 to discharge fluids from the chamber, an inlet check valve 5 normally closing the fluid inlet 2 through the action of a spring 6 between the inlet check valve 5 and an apertured platform 7 which is positioned across the chamber in the housing 1 has an annular circumferential channel 8 which communicates with the atmosphere through an opening 8a in the housing 1 through an atmospheric vent valve 9 when the platform 7 is at rest in a lower position as shown in FIG. 1. The atmospheric vent valve 9 has a sealing washer 9a on it to engage a seat on platform 7. The drain valve 10 which is positioned in the drain 4, has at its top a spray baffle 11 which is apertured at its edge to allow controlled fluid flow past it, and this drain valve 10 is loaded toward an open position by a spring 12 which is confined between the lower end of the housing 1 and the drain valve 10 but this valve also has a spring 13 between it and a push member 14 which is coupled by push rods 15 to the inlet check valve 5 so that when the inlet check valve 5 is pushed down by pressure to allow water flow into the chamber of the housing 1, the drain valve 10 is moved to a closed position by the push member 14 engaging the spray baffle 11 on the drain valve 10 so that the drain valve 10 is held shut against pressure of the spring 12 during the normal supply of pressure fluid to the inlet. The drain valve 10 has a sealing washer 10a which engages a face on the housing 1 when the drain valve 10 is closed. The outlet check valve 16 is disposed in the fluid outlet 3 at the base of the chamber 1 and is loaded by a spring 17 to a closed position, and when backflow occurs normally prevents backflow into the chamber of the housing 1, but if leakage occurs in this outlet check valve 16 under conditions where backflow would take place into the chamber of the housing 1, which happens when the inlet pressure is lower than the outlet pressure, the drain valve 10 is opened by pressure of the spring 12 but also by pressure against the spring baffle 11 which extends, excepting for peripheral bleed apertures 18, across the chamber in the housing 1 and which of course co-acts with the push member 14 and thus the push rods 15 to move the inlet check valve 5 to its closed position. The outlet check valve 16 has an "0" ring 1 6a encircling it. Disposed within the platform 7 is the atmospheric vent valve 9 which is spring loaded, there being a spring 19 between it and the platform 7 tending to open the valve, and a spring 20 which engages the inlet check valve 5 and is so balanced that when the inlet check valve 5 is closed, the atmospheric vent valve 9 is opened to allow the chamber of the housing 1 to be at atmospheric pressure, the balance however being such that the atmospheric vent valve 9 is closed during normal flow of fluid past the inlet check valve 5 to the chamber of the housing 1. The atmospheric vent valve 9 carries a sealing washer 9a. The fluid fiows through an aperture the platform 7 and through past the edges of the spray baffle 11 on the drain valve 10 but of course the drain valve 9 has its sealing washer 9a held in a closed position by the push rods 15, the push member 14 transmitting the push from the inlet valve 5 to the push member 14 and thus to the drain valve 10 to hold it in a closed position, the spring 13 between the drain valve 10 and the push member 14 ensuring that the valve is maintained in a closed position during pressure fluid flow from the inlet to the outlet. The inlet valve 5 has a sealing washer 5a and also has an "0" ring 5b which moves out of the inlet when the inlet valve is open, one purpose of this being to have a longer travel of the inlet check vale 5 to facilitate operation of the drain valve 10. The platform 7 has "0" rings 7a around to locate it but is apertured at 21 to allow the push rods 15 to pass through it and to allow fluid flow through it past the push rods 15 whereby to allow flow of fluid through the platform 7 during fluid supply to the outlet 3. Test points 22 are provided to check conditions. In this way an assembly is provided which is schematically shown in FIGS. 4, 5, 6 and 7 in which in a static position has the inlet check valve 5 and the outlet check valve 16 closed but the atmospheric vent valve 9 and the drain valve 10 are in an open position so that the chamber in the housing 1 is at atmospheric pressure and no flow can take place through it in either direction. As shown in FIG. 5 when pressure at the inlet 2 exceeds pressure at the outlet 3 the inlet check valve 5 opens and the movement of the inlet check valve 5 at the same time closes the vent valve 9 and the drain valve 10. The outlet check valve 16 opens so that fluid flow takes place through the chamber of the housing 1 so long as the pressure at the outlet remains less than the pressure at the inlet and neither pressure is less than atmospheric. FIG. 6 indicates what happens if inlet pressure falls below the back pressure, which closes the outlet check valve 16, but if this outlet check valve leaks, such leakage is allowed to flow from the outlet check valve 16 through the drain valve 10 because both the drain valve 10 and the atmospheric vent valve 9 are open under such a condition to ensure that at least the space between the platform 7 and the fluid inlet 2 is atmospheric. FIG. 7 shows how at this stage air can flow through the atmospheric vent valve 9 into the chamber of the housing 1 so that even if the inlet valve 5 leaks, there will be no backflow because of an air column between the fluid inlet 2 and the fluid outlet 3. It is of course possible to considerably vary the construction of this device but maintaining the general principle of operation which is to so arrange the valve that under normal conditions flow takes place through the valve from a supply fluid to a consumer device but if pressure falls in the supply, the inlet check valve 5 is closed and, depending on conditions, should the outlet check valve 16 leak, such fluid is drained from the chamber or the housing 1 through the drain valve 10 while the chamber of the housing I is at atmospheric pressure to ensure that there is complete separation of any flow by such flow being bypassed to the atmosphere through the drain 4 and not to the fluid supply source. OPERATIONAL DESCRIPTION Situation 1 FIG. 1 shows a cross sectional view of the valve, in the unpressurised situation, the fluid inlet check valve 5 with its sealing washer 5a and associated "0" ring 5b being held in the closed position under the influence of the spring 6. The atmospheric vent valve 9 with its associated sealing washer 9a and the drain valve 10 with associated sealing washer 1 0a are both held open under the influence of springs 19 and 12, whilst the outlet check valve 16 and its "0" ring seal 1 6a are held in the closed position by the spring 17. This situation is shown diagrammatically in FIG. 4. Situation 2 Inlet pressure positive with downstream demand cock (not shown) open. Incoming pressure will cause the inlet check valve 5 to move vertically downwards, however the internal dimensions are arranged so that sufficient force is applied to spring 20 to close the atmospheric inlet valve 9, and similarly via the push member push-rod assembly 14-15 to close the drain valve 10. Continuing movement of the inlet check valve 5 then forces the "0" ring 5b to exit the neck 2a of the housing, allowing water to flow into the chamber in the housing 1. Internal pressure then opens the outlet check valve 16 allowing water to flow to the demand point. This is shown diagrammatically in FIG. 5. Situation 3 Mains pressure drops to atmospheric or less, with outlet check valve 16 leaking and back pressure applied from the downstream supply. Back pressure leakage exists through the drain valve 10, as shown in FIG. 6. Situation 4 As for Situation 3 above, but with inlet check valve 5 also leaking. In this situation, atmospheric air will be drawn into the chamber of the housing 1 via the atmospheric vent valve 9, as shown in FIG. 7 and will exit into the mains supply system. It should be noted that the invention incorporates an inbuilt vertical air gap with an interspersed spray baffle 11, and the inlet valve 5 incorporates double protection by means of a conventional sealing washer 5a and an associated "0" ring 5b.

Claims: 1. A backflow prevention valve comprising a housing (1) having a chamber therein, an inlet (2) for fluid into the said chamber, an outlet (3) for fluid from the said chamber remote from the said inlet (2) and an inlet check valve (5) in the said inlet (2) to prevent backflow through the said inlet, characterised by: a drain (4) through the said housing to drain fluid from the said chamber in the said housing (1), a drain valve (10) in the said housing (1) to control flow through the said drain (4), coupling means (13, 14,15) between the said inlet check valve (5) and the said drain valve (10) to open the said drain valve (10) when the said inlet check valve (5) is positioned to close the said inlet (2), and an outlet check valve (16) in the said outlet (3) to prevent backflow through the said outlet. 2. A backflow prevention valve according to claim 1 wherein the said coupling means comprise at least a push rod (15) in the said chamber in the path of movement of the said inlet check valve (5), and a spring (13) in the said chamber between the said push rod (15) and the said drain valve (10). 3. A backflow prevention valve according to claim 2 wherein the said inlet check valve (5) has an "0" ring seal (5b) operating within the said inlet (2) to cause the said inlet (2) to remain closed during the initial travel of the said inlet check valve (5) when admitting fluid to the chamber of the said housing (1) to initiate closing of the said drain valve (10). 4. A backflow prevention valve according to claim 3 wherein a sealing washer (5a) is disposed on the said inlet check valve (5) to engage a seal on the said closure cap (1 a) when the said inlet check valve (5) is closed. 5. A backflow prevention valve according to claim 2 wherein the said coupling means (13, 14, 15) include an apertured spray baffle (11) on the said drain valve (10) which is disposed in the said chamber in the housing (1) between the said inlet (2) and the said outlet (3) whereby fluid flow through the said chamber influences the position of the said drain valve (10) to control flow through the said drain (4). 6. A backflow prevention valve according to claim 2 wherein a push member (14) carries push rods (15) guided in apertures (21) through a platform (7) supported in the said chamber of the said housing (1), and the said push member (14) engages a spring (13) positioned between it and the said drain valve (10) whereby to urge the said drain valve (10) toward its seat: 7. A backflow prevention valve according to claim 6 wherein a spring (12) is disposed between the said drain valve (10) and the said housing (1) to urge the said drain valve (10) into open position when the said inlet check valve (5) is closed. 8. A backflow prevention valve according to claim 2 wherein a platform (7) is disposed in the said chamber of the said housing (1) between the said inlet (2) and the said outlet (3), and an atmospheric vent valve (9) is carried by the said platform (7) and arranged to vent the said chamber to atmosphere through an opening (8a) through the wall of the said housing (1) during backflow conditions. 9. A backflow prevention valve according to claim 8 wherein a spring (19) is positioned between the said atmospheric vent valve (9) and the said platform (7), to urge the said atmospheric vent valve (9) to open, and a spring (20) is positioned between the said atmospheric vent valve (9) and the said inlet check valve (5) whereby a differential spring pressure on the said atmospheric vent valve (9) results to open the said atmospheric vent valve (9) to open the said chamber to the atmosphere when the inlet check valve (5) is closed. 10. A backflow prevention valve according to claim 1 comprising in combination: the said housing (1) having the said chamber within it, having the said inlet (2) for fluid in a first end position of the said chamber of the said housing (1), and having the said outlet (3) from the said chamber and the said drain (4) from the said chamber at a second end position of the said chamber of the said housing (1), and in the said chamber between the said first end and the said second end a platform (7) having a fluid flow aperture (21) therethrough and carrying an atmospheric vent valve (9) arranged to vent the said chamber to the atmosphere, and having the said inlet check valve (5) in the said inlet (2), and having the said outlet check valve (16) in the said outlet (3), the said drain valve (10) in the said drain (4) having a spray baffle (11) disposed between the said platform (7) and the said second end position of the said chamber, the said operative means coupling the said inlet check valve (5) to the said drain valve 10 including at least a push rod (15) and springs (6, 12, 13, and 17) whereby to move the said inlet check valve (5) to closed position and the said drain valve (10) to open position and the said atmosphere vent valve (9) to open position when fluid pressure at the said outlet (3) exceeds fluid pressure at the said inlet (2). 11. A backflow valve according to claim 10, wherein the said operative means comprise a push member (14) and at least the push rod (15) terminating in the path of movement of the said inlet check valve (5), a spring (13) between the said push member (14) and the said drain valve (10), a spring (12) urging the said drain valve (10) to open the said drain valve (10), spring means (6) to urge the said push member (14) toward the said drain valve (10), a spring (19) urging the said atmospheric vent valve on the said platform (7) toward the said inlet check valve (5), and a spring (20) between the said atmospheric vent valve (9) and the said inlet check valve (5) the arrangement being such that outflow from the said drain valve (10) to the atmosphere occurs when the pressure at the consumer source exceeds that at the supply source or when both pressures are equal but less than atmospheric at both points, and the chamber of the housing (1) is vented to atmosphere through the said atmospheric vent valve (9) when pressure of the pressure source falls below pressure at the consumer source.

Inventors: BEATTIE DAVID DOWLEY, BEATTIE, DAVID, DOWLEY
Applicants: BURNETTA PTY LTD, BURNETTA PTY. LTD.
Application year: 1989
Main classification: F16K24
IPC codes: E03C1, F16K15, F16K24