Patent ID: 8474479

Claim:
A multifunction relief valve comprising: a relief chamber having an introduction port and a relief port for introducing and relieving pressure fluid; a back pressure chamber formed on one end side of the relief chamber; a piston which is movably provided in the back pressure chamber and divides the back pressure chamber into a first back pressure chamber and a second back pressure chamber; a first spring which is provided in the first back pressure chamber and exerts a biasing force in a direction in which the relief port is closed; a second spring which is provided in the second back pressure chamber and biases the piston in the direction in which the relief port is closed; a pilot pressure supply port formed in the first back pressure chamber, and a relief chamber dividing component which is movably provided at a border between the relief chamber and the first back pressure chamber and is biased by the first spring, wherein, the relief chamber dividing component includes: a large diameter portion which opens and closes the relief port and with which the first spring is in contact; and a small diameter portion which is concentric with the large diameter portion and around which the first spring is inserted, wherein, the relief chamber dividing component and the piston are provided on a single straight line and the small diameter portion and the piston are provided on a single straight line to be able to contact each other, and wherein, when pressure fluid is introduced into the first back pressure chamber via the pilot pressure supply port, a relief pressure is changed to a low pressure, because the piston is pushed by the pressure fluid and the second spring contracts and hence the piston contacting the small diameter portion is separated from the small diameter portion of the relief chamber dividing component biased by the first spring.