UNLOADING VALVE

摘要

A spool 33 provided with a flange 39 is inserted in a spool bore 32, and a pressing force of a spring 52 is always applied through the flange 39 to the spool 33 at its one end in a second pressure chamber 35. A fluid groove 60 is formed in an inner peripheral surface of the spool bore 32 at a position near an abutment surface 51. A hydraulic fluid under the same pressure P2 as that in the second pressure chamber 35 is introduced to the fluid groove 60 through a fluid passage 61 formed in a valve body 31. When the flange 39 and the abutment surface 51 are in contact with each other, the hydraulic fluid is allowed to enter the interface between them through the fluid groove 60. A rise of the cracking pressure, which occurs upon the flange coming into tightly close contact with the abutment surface, can be prevented without reducing the strength of the flange 39, and stable opening/closing characteristics of the spool 33 can be achieved.