Double acting actuators provide bi-directional actuation for secondary mechanisms, powered by electric motors or compressed oil and gas. They are ideal for high torque loads in both directions, while single acting actuators deliver power over half of their actuation output range.
A double acting actuator is a mechanical device designed to provide powered bi-directional actuation for secondary mechanisms. This is in contrast to single acting or spring return actuators and solenoids, which have motorized travel in only one direction and rely on a secondary energy source to reset or return the actuator. The double acting actuator is typically driven by electric motors or compressed oil and gas. Electrically operated double-acting actuators provide their bi-directional force via a motor reversing control loop. Compressed gas and oil actuators have opposing inlet valves that direct the driving agent to one side or the other of the actuator mechanism.
Actuators are devices used to operate a machine or mechanism from a distance by providing a predetermined range of motion of the powered output. This motion is usually split into two strokes in opposite directions. These can be activation and recovery strokes or bi-directional operating strokes. Activation and recovery systems are well illustrated by a metal shear where the die is pushed down for the activation stroke and recovered, or returned, to a neutral position awaiting the next cycle. A bi-directional output can be seen in a valve actuator, which rotates in one direction to open the valve and in the opposite direction to close it.
There are many different categories of actuators, the most important being the double acting actuators or single acting types of actuators. The distinguishing feature between these two categories is whether the actuator supplies power for both directions of its operating range or just one. A single acting actuator will only deliver power over half of its actuation output range. This type of actuator is typically used when a torque load is experienced only on the actuating stroke – for example on the previously mentioned metal stamping machine – and the opposing stroke is only needed to return the actuator to the 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 completed.
In contrast, the double acting actuator is powered on both halves of its cycle and is ideal for applications that experience 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 direction of rotation of the drive motor. Compressed gas or oil operated actuators 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 operated in one direction, the valves send gas or oil to one side of the piston or vane in the actuator mechanism, which drives it in a certain direction. When reverse stroke is required, directional valves direct gas or oil to the opposite side of the vane or piston effectively reversing its output direction.
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