Scotch Yoke vs. Rack & Pinion: How to Select the Optimal Actuator for Large Valves

Selecting between Rack & Pinion (AT/GT series) and Scotch Yoke pneumatic actuators is one of the most critical decisions in valve automation sizing. While Rack & Pinion mechanisms generate constant linear torque throughout the entire 90° travel angle (ideal for modulating control valves and small-to-medium quarter-turn valves up to DN250), Scotch Yoke mechanisms produce a variable U-shaped torque curve. Scotch Yoke actuators deliver peak torque at 0° (breakaway) and 90° (end seating), which aligns perfectly with the unseating torque demand of high-pressure metal-seated ball and high-performance triple offset butterfly valves. Huaji provides engineered sizing calculations, CAD drawings, and mounting brackets tailored for both pneumatic and hydraulic services up to 130,000 Nm.