Patent ID: 6986362

Claim:
A pilot operated relief valve comprising: a sleeve provided with a high-pressure inlet to which hydraulic fluid from a pump is supplied, and a tank fluid channel through which the hydraulic fluid of the high-pressure inlet is returned to a tank; a main poppet provided in the sleeve so as to be communicated with the high-pressure inlet in a front thereof to allow the hydraulic fluid to be introduced into a back pressure chamber provided in a rear thereof, and to be resiliently supported by a main poppet spring to open/close the high-pressure inlet and the tank fluid channel; a seat provided with a seat fluid channel communicated with the back pressure chamber and provided in the sleeve; a housing provided with a signal inlet into which a pilot signal pressure is inputted and a tank inlet communicated with the tank fluid channel, and connected to the sleeve so as to be communicated with the seat fluid channel on a front end thereof; a pilot poppet resiliently supported to be movable in the housing by a pilot poppet spring, and provided to open/close the tank inlet and the seat fluid channel on a front end thereof; a piston movably provided in the housing to support a rear end of the pilot poppet spring, and pressing the pilot poppet spring by means of the pilot signal pressure inputted at the signal inlet; and a balance system having a balance chamber which is provided in a front of the piston within the housing and is connected with the tank fluid channel, a balance fluid channel passing through a center of the piston, and a balance back chamber communicated with the balance chamber through the balance fluid channel, and offsetting the tank pressure exerted on the piston.