Shutoff valve

A shutoff valve comprising:

• a casing having a flow passage for fluid extending in a central axis direction of the casing;
• a valve stem disposed in the flow passage and extending in the central axis direction;
• a valve body formed at a tip of the valve stem;
• a valve seat formed in the casing near an end of the flow passage;
• and
• a valve closing mechanism that presses the valve body against the valve seat, wherein said valve closing mechanism is composed of an actuator and a valve closing force adjustment mechanism;
• said valve closing force adjustment mechanism includes a pressure transmission chamber and a valve stem actuation shaft accommodating device;
• said valve stem actuation shaft accommodating device includes a valve stem actuation shaft that engages with the valve stem and is moved in the central axial direction by the actuator, and a pressure adjustment spring disposed between the valve stem actuation shaft and the actuator;
• and
• said valve stem actuation shaft is provided with a seal mechanism for preventing fluid from flowing into the actuator side.