Hydraulic control circuit with remotely controlled dual pressure relief valve

A hydraulic control circuit for operating a double-acting hydraulic jack and for providing fluid to the jack at a relatively high pressure when the jack is being operated in a selected direction, the circuit providing fluid to the jack at a relatively low pressure when the jack is being operated in the opposite direction, comprising

• a source of fluid,
• a control valve having an inlet passage in communication with the source and a movable spool means for selectively communicating opposite ends of the jack with the inlet passage and a fluid drain respectively, the jack being operated in the selected direction by fluid pressure directed to a first end of the jack from the inlet passage,
• a pilot operated dual pressure relief valve communicating the inlet passage to drain, the relief valve normally establishing the relatively low fluid pressure in the inlet passage, and
• pilot control means operatively responsive to the jack and in communication with the dual pressure relief valve to condition the relief valve for establishing the relatively high fluid pressure in the inlet passage when the spool means of the control valve is positioned to operate the jack in the selected direction,
• the dual pressure relief valve including means responsive to a hydraulic pilot signal for establishing the relatively high pressure, the pilot control means comprising a pilot valve for establishing the pilot signal communicated to the hydraulically responsive means, the pilot valve being operatively coupled with the jack to interrupt the pilot signal as the jack approaches a predetermined limit of travel in the selected direction.