The compressed air "suspended" servo motor has an air inlet chamber and an exhaust chamber sepd. by a piston. A high air pressure is maintained in both chambers when the servo motor is in its "ready for use" state. To operate the servo motor the pressure in the exhaust chamber is reduced relative to the inlet chamber to create a pressure differential across the piston. The pressure differential is controlled by a valve located in a piston passageway interconnecting the two chambers and which has an annular plunger operated by movement of an input rod to shut off the passageway. The plunger reacts against the input rod and has oppositely directed areas exposed to the exhaust chamber pressure to effect a balance on the plunger and to limit its nett reaction against the rod (18).

Alastair John Young

Papers

Compressed air servo motor - has inlet and exhaust chambers separated by piston and pressurised prior to use