Siemens 331-4821 NO. 3 PNEUMATIC ACTUATOR, 8-13 PSI, EXTENDED SHAFT MOUNTING, 2-3/4-INCH STROKESiemens 331 4821 No. 3 Pneumatic Actuator, 8 13 psi, Extended Shaft Mounting, 2 3 4 inch Stroke This 331 Number 3 Pneumatic Damper Actuator is a rugged, metal fabricated device that provides gradual or positive actuation of HVAC and fire smoke dampers. This actuator has a nominal spring range of 8 to 13 psi. Additional Information Actuator TypePneumatic Pneumatic ModelNo. 3 Spring Range8 13 psi Ball Joint ConnectorNO ClevisNO Mounting StyleExtended