Patent ID: 8011387

Claim:
A pressure control device for heavy equipment, comprising: a valve body having an input port, an output port, and a drain port, formed thereon; a spool, slidably installed in the valve body, for being shifted to connect the input port to the output port in response to a pressure obtained by adding an elastic force of a valve spring to a pressure being applied from the input port to a fluid pressure receiving portion of a first piston that is elastically supported in a first back chamber, and being shifted to disconnect the input port from the output port in response to a pressure being applied from the output port to a fluid pressure receiving portion of a second piston installed in a second back chamber; and a signal pressure port for applying a signal pressure to a fluid pressure receiving portion of the spool located in a third back chamber formed in the valve body, disconnecting the input port from the output port by shifting the spool in response to the pressure in the second back chamber and the signal pressure, and returning the pressure in the output port to the drain port; wherein the pressure control device further comprises: a first annular notch, formed on a periphery of the spool, for connecting the input port to the output port; a first passage, formed through the spool, for connecting the first annular notch to the first back chamber and supplying the hydraulic fluid fed from the input port to the first back chamber; a second annular notch, formed on the periphery of the spool, for connecting to the drain port, when the spool is shifted, corresponding to the signal pressure P 3 applied to the third back chamber; and a second passage for supplying the hydraulic fluid fed from the input port to the second back chamber, and connecting the output port to the drain port when the spool is shifted, corresponding to the signal pressure P 3 applied to the third back chamber; wherein the spool is shifted, corresponding to the signal pressure applied from an outside to the third back chamber, to control the operating pressure being applied from the input port to the output port.