Valve actuator and diaphragm valve including the same

A valve actuator comprising:

• an actuator main body;
• a repulsive member provided in the actuator main body;
• a piston pressed by the repulsive member;
• at least two air chambers arranged in the actuator main body for moving the piston by an air pressure;
• a booster mechanism accommodated in a first air chamber of the at least two air chambers for exerting a force amplified in a valve-closing direction;
• and
• an output member,
• wherein the booster mechanism is configured so that paired cam members are pivotally attached to a common swing shaft, and the paired cam members are accommodated in the first air chamber,
• wherein the paired cam members each have a contact part provided at a respective upper end part, each contact part being in contact with the piston,
• wherein the paired cam members each have a cam face formed at a respective lower end part, each cam face being in contact with the output member,
• and wherein motive power of the piston pressed by the repulsive member is amplified by the paired cam members rotating via the common swing shaft by taking the contact parts as points of effort, taking the common swing shaft as a fulcrum, and taking the cam faces as points of load, and is transferred to the output member.