Advantages of Rotary Pneumatic Actuators Over Rack & Pinion and Scotch Yoke Actuators

Rotary actuator control valve.
(Easytork)

By virtue of their design, pure rotary-to-rotary actuators experience zero repeatability loss, regardless of how long the actuator is used, making them a better choice than linear-to-rotary actuators.

The Problem

Rack and pinion or scotch-yoke actuators on the market today convert linear to rotary movement. The wear between the racks and pinion will worsen over time, increasing the repeatability losses. Rack and pinion, and diaphragm actuators, all require gears to convert linear motion to rotary motion, adding rack and gearing tolerances which add backlash or hysteresis. Over time, wear in the rack and gearing areas add additional backlash or hysteresis, degrading the actuators repeatability.

The Solution

Pneumatic vane actuators are pure rotary-to-rotary, meaning all motion produced by the vane actuator transfers unfiltered to the valve stem with zero motion loss. Unlike linear-to-rotary actuators, where the pinion experiences wear and lost motion which leads to increased backlash over time, rotary-to-rotary designs do not have to contend with the increased backlash.

For more information, contact:
Process Control Solutions
https://flowcontrol.processcontrolsolutions.com
(800) 462-5769

Rotary Actuators in Fluid Power Systems

A rotary actuator is an output device for a fluid power system that delivers an oscillating motion over a limited range in less than one full revolution of the circle.

A true rotary actuator produces work by direct action of fluid pressure against internal vanes. Work is defined as a force applied over a distance. Rotary actuators produce a special type of rotational work called torque.

Torque occurs when a force acts on a radius. Since rotary actuators operate at low speed with high torque, torque output rather than the horsepower is used for the rating and identification purposes. Speed is a secondary consideration when choosing a rotary actuator for a particular application.

The typical units of measurement for torque are foot pounds (lb·ft). For example, if a rotary actuator with an arm length or radius of two feet were used to lift the two hundred-pound weight, then the resultant torque required to accomplish the work would be 400 lb·ft.

Understanding the relationship between the output torque required and the physical set up a fluid system enables designers to determine the appropriate rotary actuator for each unique application.

The video below illustrates the mechanics and the physics behind rotary actuators.