Importance

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Abstract

A relief valve to be disposed in a hydraulic circuit, for example an absolute circuit, such as in an industrial construction machine, comprises a casing of substantially cylindrical structure having one end and another end, the casing including a casing body, a pressure regulating plug and a lid member. The relief valve further comprises a valve seat fitted into one end of the casing and provided with an inflow hole through which a pressurized fluid is flown, a plunger disposed in the casing and having one flanged end slidably engaged with an inner surface of the one end of the casing, the plunger having a central through hole, a stepped piston member disposed in the casing to be slidable therein and having an outwardly stepped one end and a spring member disposed between another end of the stepped piston member and the flanged one end of the plunger. A fluid chamber is defined between another end of the casing and the one end of the stepped piston member. A damping chamber is defined between the stepped portion of the stepped piston member and the stepped portion formed to the casing. The fluid chamber and the damping chamber is communicated with each other through a communication passage. The through hole of the plunger having a throttle portion having a predetermined length and the other end of the stepped piston member having an outer diameter substantially equal to an inner diameter of the inflow hole of the valve seat.

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First Claim