Oil-pressure-controlling device for big inertial load

Claim 1

An oil-pressure-controlling device for a hydraulic motor coupled to a large inertial load comprising: a valve body including first and second independent bores formed therein, a first pair of inlet and outlet ports hydraulically coupled to said first bore and hydraulically connected respectively to a source of pressurized oil and a tank through a directional control valve, a pair of annular chambers hydraulically coupled to said second bore and connected to intake and exhaust passages to said hydraulic motor, a slidable valve seat cylinder carried by said second bore between said pair of annular chambers and axially slidable between limits and defining a common bypass passage between said intake and exhaust passages of said hydraulic motor, plungers carried by said second bore on opposite sides of said valve seat cylinder, springs biasing each plunger in pressure contact with the respective ends of said slidable valve seat cylinder, the oil pressure of either said intake or exhaust passage of said hydraulic motor upon reaching a predetermined value causes the valve seat cylinder to slide to a predetermined limit position to open the bypass passage between the exhaust and intake passages of said hydraulic motor, a high-pressure crossover relief valve means for each plunger, a slidable valve spool carried by said first bore, poppet valves operatively associated with the slidable valve spool and said intake and exhaust passages to said hydraulic motor to insure that regardless of the position of the directional control valve, the exhaust oil passage is automatically opened or closed, depending upon the pressure of the oil in the hydraulic motor exhaust passage.