Patent ID: 7698991

Claim:
A spring-return, pneumatic actuator comprising: a casing having an air supply and exhaust vent; a piston arranged within said casing, said piston being configured to move due to air supplied and discharged from said air supply and exhaust vent on a primary side of said piston; a piston rod connected to said piston; a conversion mechanism for converting a reciprocating linear motion of said piston into a rotary motion; a spring for undergoing a snap action for applying a spring force against said piston during reciprocating motion of said piston; a sealed communication space chamber comprising a spring chamber housing said spring and a secondary side chamber of said casing located at a secondary side of said piston, said sealed communication space chamber having communication parts to allow said spring chamber to communicate with said secondary side chamber, said communication space chamber being sealed and having a predetermined volume such that a rise in pressure during the reciprocating motion of said piston is no greater than 0.02 MPa; and a check valve communicating with said sealed communication space chamber to allow only escape of air from inside said sealed communication space chamber if a set pressure is reached or exceeded within said sealed communication space chamber.