Double check valve backflow preventer assembly

A double check valve backflow preventer assembly for installation in a liquid supply line in a space of predetermined length dimension between a pair of gate valve assemblies normally occupied by a single check valve backflow preventer assembly, said double check valve backflow preventer assembly comprising:

• a single unitary valve body having substantially said predetermined length dimension and opposite end coupling means for coupling to corresponding coupling means of said gate valve assemblies and defining opposite end liquid inlet and outlet openings;
• said valve body defining a single access opening between said opposite end inlet and outlet openings and a removable access cover for closing said access opening,
• a first annular valve seat within said valve body on the inlet side of said access opening,
• a second annular valve seat within said valve body on the outlet side of said access opening,
• a first check valve assembly for mounting within said valve body to open in a downstream direction with respect to said inlet and outlet openings and including a first stationary valve cage having a ring for seating against said first valve seat,
• a second check valve assembly for mounting within said valve body to open in a downstream direction with respect to said inlet and outlet openings and including a second stationary valve cage having a ring for seating against said second valve seat,
• and releasable seating means operable to seat said first valve cage ring against said first valve seat and said second valve cage ring against said second valve seat, said seating means being operable to seat and release said cage rings from their seated engagement with said valve seats through said single access opening,
• said seating means comprising compression means extending between said first and second valve cage rings to compress said rings against their respective valve seats.

A valve body for a double check valve backflow preventer valve assembly having a pair of check valves arranged in series to permit fluid flow in the same direction, the valve body comprising:

• a single unitary body member having opposite inlet and outlet end coupling means defining flow inlet and outlet openings, said openings defining a common flow axis and said body member defining a generally straight flow path,
• said body member defining a single access opening between said inlet and outlet end openings and substantially closer to said inlet opening than to said outlet opening, the access opening being generally normal to the flow path,
• said body member having a predetermined length corresponding to the length of the body member of a single check valve backflow preventer assembly of corresponding diameter,
• and a pair or annular check valve seats, one on each of opposite sides of said access opening and both closely adjacent to said opening,
• each of said valve seats defining an annular seat surface in a plane generally normal to the flow path,
• the annular seat surface of each valve seat of said pair facing the annular seat surface of the other valve seat of the pair, such that a pair of check valve assemblies can be inserted into said valve body through said access opening and urged one against one valve seat surface and the other against the other valve seat surface by a common compression means acting in opposite directions against said valve assemblies.

In a backflow preventer valve assembly including a valve body and a pair of check valve assemblies mounted in series within said body, said body defining inlet and outlet openings and a pair of annular valve seat surfaces spaced apart in the direction of flow through said body and an access opening into said body between the valve seat surfaces each check valve assembly comprising:

• a cage member for stationary mounting within said body, said cage member including a peripheral cage ring for seating against one of said annular valve seat surfaces within said body, a central cage cylinder, and cage arms interconnecting said cylinder and ring,
• a guide member connected to and radiating from said cylinder, a piston movable within said cylinder from a closed end of the cylinder, a piston rod connected to said piston and movable through an opposite end of said cylinder, and a closure spring means within said cylinder urging said piston to said closed end,
• a cup-like closure member in surrounding relationship to said cage cylinder and guide member and having an annular rim at an open end thereof in sealing engagement with the cage ring in a closed position of the closure member and an opposite end wall overlying the opposite end of said cylinder and connected to said piston rod such that said closure spring urges said closure member in one direction toward said closed position against fluid pressure acting against said closure member in the opposite direction,
• the cage cylinder and cup-like closure member of each assembly when mounted in said body against its associated valve seat surface being positioned downstream of its associated valve seat surface and cage ring.