Relief valve

A relief valve, comprising:

• a case having a forward end and a rearward end, and an inner bore, and an opening defining an outlet;
• a valve seat adjacent to forward end of the case, the valve seat defining an inlet;
• a spring, disposed within the case;
• a first liquid chamber;
• a second liquid chamber;
• a third liquid chamber;
• a plunger slidably disposed within the case and pressed forward by the spring to shut off fluid communication between the inlet and the outlet, and which moves rearwardly against elastic force of the spring with an increase in fluid pressure at the inlet, thereby making the inlet and outlet communicate with each other;
• a piston slidably disposed within the case, and slidably receiving the plunger, the piston being configured for pushing forward a rear end of the spring, which piston moves forward with the increase in the pressure at the inlet to compress the spring, thereby regulating a relief pressure;
• a liquid chamber defined by the case accommodating the spring therein, and which fluidly communicates with the outlet;
• wherein the piston further comprises a first sliding portion configured for sliding with liquidtightness in the inner bore of case, and a sliding bore formed along a central axis of the piston, and wherein a rear portion of the plunger is slidably inserted and fitted in the sliding bore formed along a central axis of the piston, and the plunger further comprises a through hole configured for feeding a pressurized liquid from the inlet to the rear of the plunger, and
• wherein the third liquid chamber is defined by a space of a rear portion of the sliding bore that the plunger does not reach and the through hole,
• and wherein the piston further comprises a rearward acting face and a forward acting face provided rearward from the first sliding portion of the piston,
• and wherein the third liquid chamber and the first liquid chamber on which the rearward acting face fronts communicate with each other through a communicating hole formed in the piston, and the third liquid chamber and the second liquid chamber on which the forward acting face fronts communicate with each other through a communicating hole formed in the piston, and
• the piston moves forward by a difference between the combined rearward acting force given to a bottom face of the sliding bore and the rearward acting face by the pressurized liquid, and the forward acting force given to the forward acting face by the pressurized liquid.