What is a Scotch Yoke Pneumatic Valve Actuator?

According to Wikipedia, "The Scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part. The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed."

Animation of Scotch Yoke (courtesy of Wikipedia)

In a pneumatic actuator, the scotch yoke mechanism converts linear motion (provided by an air supply and pistons) to rotary motion. A return spring sets the rotation in the opposite direction.

Diagram of Scotch Yoke Internals (courtesy of ROTEX Controls)

Scotch yoke mechanism provides a great torque curve for many valve types and are most often used on larger valves. Additionally, as valve torque requirements increase, a scotch yoke actuator becomes a more economical choice considering production cost.

The disadvantages of scotch yoke actuators are typically the wear and tear on the pin and bearing mechanism. Manufacturers like ROTEX Controls have reduced this issue with innovative design improvements that reduce friction and wear.

ROTEX Controls DRS Scotch Yoke Actuator