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What Is a Double Acting Actuator?

Paul Scott
Paul Scott

A double acting actuator is a mechanical device designed to supply powered bi-directional actuation for secondary mechanisms. This is in contrast to single action or spring return actuators and solenoids, which feature a powered stroke in one direction only and rely on a secondary source of energy to reset or return the actuator. The double acting actuator is typically driven by electric motors or compressed oil and gas. Electrically-driven double action actuators supply their bi-directional force by means of a motor reversing control circuit. Compressed gas and oil actuators feature opposed inlet valves that direct the motive agent to one side or the other of the actuator mechanism.

Actuators are devices used to operate a machine or mechanism remotely by supplying a predetermined range of powered output movement. This movement is generally broken down into two strokes in opposed directions. These may be activation and recovery strokes or bi-directional operating strokes. Activation and recovery systems are well-illustrated by a metal stamping machine where the die is pushed down for the activation stroke and recovered, or returned, to a neutral position in readiness for the next cycle. A bi-direction output may be seen in a valve actuator, which turns in one direction to open the valve and in the opposite direction to close it.

Woman holding a book
Woman holding a book

There are many different categories of actuator, with double acting actuator or single acting actuator types being the most important. The defining characteristic between these two categories is whether the actuator supplies the power for both directions of its working range or only one. A single acting actuator will only supply power for one-half of its range of actuation output. This type of actuator is generally used where a torque load is experienced only on the activation stroke — for example, on the previously mentioned metal stamping machine — and the opposite stoke is only required to return the actuator to a neutral position. Good examples of these are spring return actuators and solenoids where the actuator is reset by spring tension once the powered stroke is complete.

In contrast, the double acting actuator is powered on both halves of its cycle and is ideal for applications that feature high torque loads in both directions, such as the valve actuator mentioned earlier. Achieving this double action in an electrically-driven double acting actuator simply involves reversing the rotational direction of the drive motor. Actuators driven by compressed gas or oil are a little more complex, and require a set of directional valves on the supply and two inlet ports on the actuator mechanism. When the actuator is driven in one direction, the valves send the gas or oil to one side of the piston or vane in the actuator mechanism, which drives it in a certain direction. When the reverse stroke is required, the directional valves direct the gas or oil to the opposite side of the vane or piston effectively reversing its output direction.

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