Importance

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Abstract

This invention provides a pressure control valve 20 including a valve plug 30 facing a seat As at a relief port A that communicates with a pressure circuit 46, and a spring 32 pressing the valve plug 30 against the seat, and when the fluid pressure in the pressure circuit surpasses the force of the spring 32 for the valve plug, the pressure control valve discharges part of the fluid to keep the interior of the pressure circuit at a specified setting pressure. In the pressure control valve, at one end of the spring for the valve plug which is remote from the valve plug there is provided a pilot piston 40 freely movable in the expansion and compression direction of the spring for the valve plug. There is also provided a spring for adjustment 38c urging the pilot piston 40 toward the valve plug side. The pilot piston 40 is so structured as to move in a direction of going away from the valve plug when supplied with a pilot fluid under a specified pressure P.sub.pi.

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First Claim