Relief valve

A relief valve comprising:

• a housing including a pilot chamber and an oil chamber therein;
• a valve body to allow or block communication between an inflow passage into which hydraulic oil flows and an outflow passage through which the hydraulic oil flows out, the valve body including a first surface facing the inflow passage, a second surface facing the oil chamber, and a through passage connecting the first surface to the second surface;
• an urging member to urge the valve body toward the inflow passage;
• and
• a piston including a first piston member to press the urging member using a pressure of pilot oil in the pilot chamber to change an amount of deflection of the urging member;
• wherein
• the first piston member is at least partially located within the oil chamber, and is operable to divide the oil chamber into a first oil chamber and a second oil chamber;
• and
• the first piston member includes a first pressure receiving surface to receive a pressure in a first axial direction of an axial direction from the hydraulic oil in the first oil chamber, and a second pressure receiving surface to receive a pressure in a second axial direction of the axial direction from the hydraulic oil in the second oil chamber.