Automatic changeover valve

Claim 1

An automatic switchover valve for changing from a depleted to a full pressure supply, comprising a casing having a bore, said bore having a discharge outlet, separate high-pressure fluid inlets laterally disposed with respect to said discharge outlet, a piston laterally movable in said bore past said outlet and alternately closing one of said high-pressure fluid inlet, seal means adapted to seal the periphery of said piston within said bore whereby fluid is prevented from leaking along the periphery of said piston, said piston having oppositely extending pins insertable within the respective high-pressure inlets to seal off the respective inlets, and means venting the respective ends of said bore to each corresponding high-pressure inlet when said corresponding high pressure inlet is closed by said piston, each venting means comprising a passage communicating with the respective high-pressure inlet to allow fluid to be released from within said bore and an O-ring blocking said passage, said O-ring being responsive to an increase in pressure within said bore to displace said O-ring whereby fluid is allowed to flow past said O-ring.