ST Series Pneumatic Actuators: Nine Structural Features Explained

Image: ST series pneumatic actuators (double acting / spring return, site archive)

ST series rack and pinion pneumatic actuators cover both double-acting and single-acting (spring-return) types in a complete size range, matching butterfly, ball and plug valves for on-off and modulating duties across oil & gas, chemical, power and water industries. Nine structural features define the design:

· Indicator: NAMUR-standard indicator for easy mounting of position switches, positioners and other accessories;
· Output shaft: nickel-plated alloy steel, high-precision one-piece output shaft conforming to NAMUR, ISO 5211 and DIN 3337 — custom dimensions and stainless steel available on request;
· Cylinder: ASTM6005 die-cast aluminium cylinder with hard anodising, epoxy coating, PTFE coating or nickel plating options for different corrosion requirements;
· End caps: die-cast aluminium caps with metal powder coating (various colours), PTFE coating or nickel plating;
· Pistons: double-piston rack design in hard-anodised cast aluminium or zinc-plated cast steel — symmetric mounting, swift operation, long life; simply reversing the pistons changes the direction of rotation;
· Travel adjustment: two independent adjustment screws allow convenient and precise ±5° setting of the switch positions;
· High-performance springs: premium coated spring material, pre-loaded in assembly — corrosion-resistant and long-lasting; single-acting actuators can be safely serviced, and changing the number of springs adapts the torque output range;
· Bearings and guides: low-friction, long-life composites avoid metal-to-metal contact, with easy maintenance and replacement;
· Seals: NBR for ambient temperatures; FKM or silicone rubber for high or low temperatures — seal material selected to suit the media and environment.

We supply the full ST series range together with solenoid valves, limit switches, positioners and other accessories — contact us for selection advice.