Backflow prevention devices

Claim 1

A backflow prevention device comprising first and second shut-off valves, first and second spring operated check valves and a differential pressure relief valve, said first shut-off valve being connected on its upstream end to an inlet pipe and on its downstream end to said first check valve, said first check valve being connected on its downstream end to said second check valve, said second check valve being connected on its downstream end to said second shut-off valve and said second shut-off valve being connected on its downstream end to an outlet pipe, said relief valve being communicatingly interconnected between the upstream end of said first check valve and said downstream end of said first check valve to provide pressure relief on the downstream end of said first check valve when a backflow condition occurs in said device, said differential pressure relief valve comprising a valve body having an inlet communicatingly connected to said downstream end of said first check valve, an outlet port and first and second valve seat areas, a diaphragm mounted in said body and a moveable valve assembly also mounted internally of said body for movement in an axial direction thereof and in position to be operatively engaged by said diaphragm, said moveable valve assembly including: (a) a retaining member having one surface operatively engageable with said diaphragm and having concentric first radially inner and first radially outer annular collars on its opposed surface with a first annular channel being formed between said first and second collars; (b) a first sealing ring positioned in said first channel, said first sealing ring having a first portion and a movable portion; (c) a first guide member having one surface abutting said first portion of said first sealing ring for retaining said ring in said first channel and having concentric second radially inner and second radially outer annular collars on its opposed surface with a second annular channel being formed between said inner and outer collars; (d) a second sealing ring positioned in said second channel; (e) a second guide member having a surface abutting said second sealing ring for retaining said ring in said second channel; and (f) means for fastening the assembly together for cooperative piston motion including a central shaft engagingly fitted through central apertures in said retaining member and said first and second guide member; said valve body further including first and second annular seat flanges positioned in said first and second valve seat areas, respectively, for engagement with and disengagement from said first and second sealing rings to control fluid flow from said inlet port to said outlet port through said first and second valve seat areas, said moveable assembly being biased by a spring in said valve body to a normally open position wherein said first sealing ring is axially spaced from said first valve seat flange and said second sealing ring is axially spaced from said second valve seat flange, means for introducing differential pressure from said upstream and downstream ends of said first check valve into said valve body on opposing sides of said diaphragm whereby said diaphragm causes said moveable assembly to move into a closed position when said differential pressure is above a first predetermined level wherein said first valve seat flange sealingly abuts said first sealing ring and said second valve seat flange sealingly abuts said second sealing ring, and whereby said diaphragm causes said movable assembly to move into an opened position when said pressure differential is below a second predetermined level, said second valve seat area opening prior to said first valve seat area opening under certain pressure conditions, a projecting annulus included in said valve body, said projecting annulus circumferentially surrounding the outer periphery of said second radially outer collar of said first guide member in close concentric proximity thereto whereby a lift chamber is formed in the second valve seat area which provides an added force on the moveable assembly to cause accelerated opening of the valve to its fully open condition once it has partially opened.