Normally closed three-port valve

A normally closed three-port valve includes a valve member urged in a valve closing direction by a return spring from a supply port side toward a main valve seat provided in a valve body between an output port and the supply port;

• a discharge channel provided into a valve opening rod which makes the main valve seat open by applying a valve opening operating force to the valve member, and the discharge channel closed by bringing the rod into contact with a discharge seat surface on the valve member;
• and a balance mechanism configured to balance the fluid pressure acting on front and back surfaces of the valve member by providing a vent hole in the valve member when the valve member is at a valve open position, and the vent hole allowing a back pressure chamber of a back of the valve member to communicate with a channel for a main fluid on the output port side,
• wherein the valve member comprises a valve member main body that is slidably held in a contacting and separating direction relative to the main valve seat and has a through hole formed therein to form the vent hole, a seat member that is formed of a discoid sealing member having rubber elasticity, that brings into contact with a main valve seat facing surface of the valve member main body, that has a main seat surface at a portion facing the main valve seat, that has the discharge seat surface formed at a portion facing an end surface of the discharge channel of the valve opening rod, and that has a communication hole allowing the through hole of the valve member main body to be open at a region between the main seat surface and the discharge seat surface, a securing member that is airtightly fitted into a central portion of the seat member so that a tip end thereof is locked in the valve member main body so as to secure the seat member to the valve member main body, and a pressing frame that holds a circumference of the seat member on the valve member main body, and
• wherein respective members are formed by molding.