Piston Actuator, Control ValvesEmerson Process Management’s Fisher 685 double-acting piston actuator is designed to provide high thrust output for short-to-long travel applications. The actuator supports both medium and large Fisher sliding-stem control valves, including the easy‑e and FB series, and is suitable for general, severe, and critical service applications. The range includes piston diameters from 305 mm to 660 mm and travel from 25 mm to 610 mm as standard, with special constructions available up to 1,118 mm piston diameter. The actuator has a maximum thrust capability of 351.4 kN (79,000 lbf) available at 10.3 barg supply pressure.