Safety lock-out valve

Claim 1

A safety system for fluid operated motors receiving pressure from an upstream fluid pressure source which comprises: a. a fluid passage leading from an upstream pressure source to a downstream fluid operated motor, b. a cut-off valve in said passage movable from a position closing said passage to a position opening said passage, c. a safety valve structure in said passage between said cut-off valve and said fluid operated motor comprising: d. a housing having a cylindrical recess open at both ends to said passage, said recess having a first bore at the upstream end and a larger concentric bore at the downstream end terminating at an annular wall around an outlet opening, e. a valve plug in said recess comprising a cup-shaped element having a restricted opening in the bottom to register with said outlet opening, and a larger, relatively-unrestricted, opening off center from said outlet opening and open to said annular wall, said element having stepped diameters to have a sliding seal fit with the respective bores of said cylindrical recess and to provide differential effective pressure areas at opposite ends of said element within said bores, and f. means biasing said valve plug toward said annular wall wherein said valve plug will permit an initial minimal flow of fluid under pressure to said outlet opening through said restricted opening and wherein said valve plug will be shifted by action of differential pressure on the effective end areas of said element to open said larger opening to said outlet opening when pressure is developed downstream of said safety valve sufficient to safely operate said fluid motor.