Linear

Linear pneumatic actuators are used on control and shut-off valves where stem movement is axial rather than rotary. Instrument air pressure is converted into linear travel to operate globe control valves, on/off valves, and throttling devices in steam, water, thermal oil, air, and other process fluid systems.

This category includes the ARI DP pneumatic actuator, based on a compact diaphragm-cylinder design, suitable for installation in any position, with a maximum air supply pressure of 6 bar. Stroke is available up to 120 mm. Functional versions include spring return on air failure, either stem extending or stem retracting. For DP32-DP34 models, direct-acting and reverse-acting configurations are specified.

Available actuator sizes cover different thrust requirements, from DP30 at 2000 N up to DP34T at 47100 N. Standard ambient temperature range is -10 °C to +80 °C, with optional low-temperature execution down to -50 °C for selected types. Materials include stems in X20Cr13+QT, 1.4021+QT, or 1.4571, with EPDM, NBR, or 42CR sealing elements and an NBR reinforced diaphragm.

Selection should be based on required shut-off force, valve stroke, available instrument air pressure, fail-safe position, response time, positioner compatibility, and any requirement for a manual handwheel. In modulating service, stem friction, packing load, valve differential pressure, and the accuracy of analog feedback have a direct effect on control stability, hysteresis, and seat leakage performance. Actuator sizing should be checked against valve shut-off class, service temperature, packing friction, and the force margin required at end position.