PILOT OPERATION TYPE PRESSURE CONTROL VALVE

PURPOSE:To prevent any over-load of a hydraulic pump and innecessary power consumption by housing an unload mechanism in a pilot valve, in a device which is formed in such constitution that a valve body provided with an area ratio on the pressure receiving surface for a pilot fluid and a main circuit fluid is opened/closed so as to control the main circuit fluid. CONSTITUTION:A relief valve 14 is formed by exchangeably assembling a valve body 15, a valve cylinder 16 and a spring 17 on the abutting surface of first and second cabinets 1, 2, and a proportional electromagnetic type pilot valve 30 and a series shaped flow regulating valve 40 are provided in the second cabinet 2. The flow regulating valve 40 is operated so as to maintain a pressure difference between both sides of an orifice 46 at a constant level at all times, pressure fluctuation of the pilot fluid is guaranteed, and input pressure into the orifice 46 is controlled to a pressure which is obtained by adding a summation value determined by the spring constant of a summation spring 43 to set pressure. An unload mechanism 80 is enclosed in the pilot valve 30 so as to switch unload condition to pressure control condition by switching a switching circuit 83 accompanying with sliding motion of a plunger 35.