Pressure-responsive fluid controlling system

Claim 1

A control system for a tool driven by fluid under pressure effective to shut-off said tool when a predetermined back pressure is encountered By said control system caused by said tool encountering a predetermined load, but not responsive to momentary back pressure surges of less than said predetermined back pressure, said control system comprising, in combination, a fluidtight valve housing, a fluid inlet port connecting a fluid pressure source to said housing, a fluid outlet port from said housing connected to an air motor driving said tool, a valve piston within said housing movable between (1) an open position at which fluid may pass from said inlet port through said housing to said outlet port and (2) a closed position at which communication between said inlet and outlet ports is shut off, means biasing said valve piston toward its said open position, said valve piston having a head and a secondary piston head of reduced area protruding from said head through an orifice plate at one end of said valve housing into an accumulator chamber, said chamber having a volume sufficient to prevent a temporary air surge from reaching said predetermined back pressure value, restricted means connecting said outlet port to said accumulator chamber whereby pressure therein will increase in response to increased back-pressure caused in said motor but at a rate slower than the initial back-pressure increase at the outlet port, said orifice plate separating said accumulator chamber from said valve pistonhead with its orifice closed by said secondary pistonhead of said valve piston when in said open position such that pressure in said accumulator chamber bears against said secondary piston of said valve piston to urge said piston against said bias means toward said closed position, and a holding port positioned to apply line pressure to said valve pistonhead when said valve piston reaches its said closed position whereby, when said back pressure reaches said predetermined value in accordance with the load on said tool, the force of said back pressure in said accumulator on said secondary pistonhead is sufficient to move said piston from its said open position to expose said valve pistonhead to said accumulator pressure and whereby continued movement of said piston toward said closed position will open said holding port such that line pressure is applied to said pistonhead to hold said piston in a closed position.