Pneumatically-actuated valve

A pneumatically-actuated valve comprising:

• a valve body;
• a shaft connected to the valve body;
• a spring member that is provided inside a valve casing and applies an axial force to the shaft in an axial direction of the shaft;
• a valve-actuating pressure chamber that is provided inside the valve casing and actuates the valve body by applying a force resisting the axial force to the shaft;
• and
• an axial-force adjusting device that has a plurality of screw members and a ring-shaped spring retainer, the plurality of screw members being provided to be inserted through the valve casing, the spring retainer being provided inside the valve casing and coming into contact with one end of each of the plurality of screw members, in which the plurality of screw members face the spring member with the spring retainer interposed therebetween, and that adjusts the magnitude of energy stored in the spring member, via the plurality of screw members, from the outside of the valve casing,
• wherein the spring member is disposed around an axis of the shaft,
• wherein the plurality of screw members are arranged at regular intervals in a circumferential direction of the spring member, and thereby apply equal loads to the spring member,
• wherein a spring accommodating chamber that is airtightly partitioned off from the valve-actuating pressure chamber and accommodates the spring member is provided inside the valve casing, and
• wherein each screw member of the plurality of screw members is threadedly engaged with a respective screw hole that allows the outside of the valve casing and the spring accommodating chamber to communicate with each other therethrough,
• wherein the pneumatically-actuated valve further comprises a gas purge port that allows a purge gas to be introduced into the spring accommodating chamber therethrough so as to gas-purge the inside of the spring accommodating chamber,
• wherein a gap is formed between each screw member of the plurality of screw members and the respective screw hole, and
• wherein the purge gas introduced into the spring accommodating chamber flows out to the outside of the valve casing via the gap.