Shutoff valve construction particularly for high pressure

Claim 1

A shutoff valve or high pressures, particularly for high pressure spray guns, comprising a housing having an inlet passage, a discharge passage communicating with said inlet passage for the flow of fluid through said inlet passage and out said discharge passage, a valve seat defined between said inlet passage and said discharge passage, a differential piston movable in said housing between a closed position on said valve seat and closing said valve to close off the flow of fluid and to an open position spaced from said valve seat to open said valve, means defining a first control chamber on the side of said differential position opposite to said valve seat, a by-pass extending from said control chamber to said discharge passage having a second control chamber therein, first control valve means in said first control chamber including a first control member separately movable to an opened position to open said first control valve means and to communicate said first control chamber with said by-pass passage, second control valve means in said second control chamber including a second control member spaced apart from and movable separately from said first control member to an open position to open the said bypass passage and permit flow of fluid therethrough, said piston valve being movable to an open position only when both said first and second control members are moved to an open position.