Pressure regulating valve with piston

A pressure regulating valve comprising:

• a body forming a pressure regulating chamber for regulating a pressure of a working liquid;
• an attachment hole provided in the body and fluidly coupled with the pressure regulating chamber;
• a valve seat assembly fitted in the attachment hole and forming a surplus liquid discharge path for discharging the working liquid in the pressure regulating chamber;
• a piston partially positioned inside the pressure regulating chamber, the piston configured to:
• contact the valve seat assembly in order to close an opening of the surplus liquid discharge path when the pressure of the working liquid is equal to or lower than a set pressure;
• and
• separate from the valve seat assembly in order to open the opening of the surplus liquid discharge path when the pressure of the working liquid exceeds the set pressure;
• and
• a valve seat seal located in the attachment hole and positioned between the body and the valve seat assembly, and configured to form a seal in a liquid-tight manner between the body and the valve seat assembly,
• wherein the valve seat assembly comprises:
• a return flow path opening provided in an outer peripheral surface of the valve seat assembly at a position facing an inner peripheral surface of the attachment hole;
• and
• a return flow path fluidly coupling the return flow path opening and the surplus liquid discharge path, and
• wherein the valve seat seal is located between the return flow path opening and the pressure regulating chamber, and
• wherein the valve seat seal is located between the body and the valve seat assembly.