RELIEF UNLOAD VALVE

PURPOSE:To perform both functions of a relief valve and an unload valve by guiding the fluid pressure of the pressure passage to the end face of a piston and providing a pilot passage separating a regulating valve plug from a valve seat. CONSTITUTION:A pilot passage 100 communicated to both through holes 77, 89 is provided on a main body 61 between the through hole 77 of a poppet 62 and the through hole 89 of a sleeve 86. The outlet 66 of a pressure passage 67 and the piston 97 of the sleeve 86 are communicated by the pilot passage 100, the fluid pressure of the pressure passage 67 is applied to the piston 97, and a regulating bar 63 is separated from a valve seat 78. Accordingly, when the peak pressure moves the regulating bar 63 upward, a tank passage 71 is communicated to a tank port 68, thus this valve can perform both functions of a relief valve and an unload valve with a simple structure.