Decompression valve

A decompression valve in which a valve mechanism housed in a body comprises a valve body that can be seated on a valve seat facing a valve chamber into which high pressure fluid is introduced, and a valve shaft that has one end linked to a pressure receiving member operable in association with pressure of a decompression chamber communicating with a valve hole surrounded by the valve seat and that extends through the valve hole while having the other end facing a back pressure chamber communicating with the decompression chamber, the valve body being fitted around the outer periphery of the valve shaft,

• wherein
• the valve body is fitted around the outer periphery of the valve shaft while allowing circulation of fluid between the valve chamber and the back pressure chamber via a space between the valve body and the valve shaft, and
• an annular seal member present between the valve chamber and the back pressure chamber is disposed between a guide member and the outer periphery of the valve body, the guide member being fixed to the body so as to guide movement, in an axial direction, of the valve shaft,
• wherein the seal member is mounted on the guide member to be in resilient sliding contact with the outer periphery of the valve body,
• a valve body mounting shaft portion having a retaining groove on an outer periphery of one end thereof is provided in part of the valve shaft, and the valve body is fitted over the valve body mounting shaft portion and resiliently engages with the retaining groove at an annular projection provided at one end thereof,
• the valve body mounting shaft portion is formed so as to have the same cross-sectional shape over a whole axial length thereof apart from a section of the retaining groove, and
• a main portion of the valve body including the portion placed in sliding contact with the seal member has a thickness smaller than that of the seal member.