In numerous instances, the benefits of double-acting actuators outweigh those of spring-return actuators.
FREMONT, CA: Actuators transform process inputs into mechanical action, opening or closing valves to regulate the flow of fluids. These devices are available in different shapes and sizes to facilitate the automation of various piping systems. Actuators improve the precision and accuracy of processes because they provide the smooth operation of valves regardless of cycling requirements. When selecting valves for specific applications, actuation mechanisms must be taken into account. In industrial pipe systems, electric, pneumatic, and hydraulic actuators are popular valve actuators.
Pneumatic and hydraulic actuators manipulate the position of a valve based on the pressure of air or fluid. Actuators go into either the spring return or double-acting groups. Actuators with spring return are single-acting. Therefore, any portion in this text that mentions single-acting actuators will refer to spring return actuators.
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A spring return actuator retains the valve in the desired position by having a spring on one side of the piston. These actuators can be configured as generally closed or normally open. In a typically closed configuration, also known as fail-closed, the unloaded side of the piston receives the force from the pressurized air or oil. The pressure fluid's force overcomes the spring force, causing it to compress and open the valve. Removing the pressurized fluids causes the spring to retract and the valve to return to its closed position. The inverted structure of this arrangement maintains the valve in the normally open position. The valve is closed when fluid pressure is applied, whereas fluid pressure withdrawal causes the spring to open the valve.
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A double-acting actuator, in contrast, comprises two compartments for pressurized fluids. One end of the container is the pressurized fluid intake, while the other is the exhaust. Introducing pressured fluids into the cylinder sections modifies the position of the piston, hence altering the valve's position. Compared to single-acting actuators, double-acting actuators allow greater control over the flow rates of valves.
When fluid pressure or power is lacking, spring-return actuators can instantly retract and restore the valves to their original positions. However, they have several disadvantages, making double-acting actuators a popular alternative for several operations. Pipeline systems can benefit from double-acting actuators in the areas listed below.
Better thrust strength: Overall, large pipe systems necessitate huge valves requiring high actuation forces. To enhance the dependability and responsiveness of these valves, reducing the actuating mechanisms' resistance is essential. Technically, the presence of a spring in a single-acting actuator decreases its thrust strength. The actuators of single-acting valves must be larger to counteract the torque of the valve and the spring forces. It translates to oversizing the single-acting actuators, necessitating additional material for the actuator's construction and increasing its price. Additionally, the springs increase the bulk of the actuators, making them considerably heavier than their double-acting equivalents.
A double-acting actuator provides maximal actuation forces in both the forward and reverse directions. Double-acting actuators have a lower thrust requirement than single-acting actuators. Double-acting actuators are preferred for highly demanding industrial pipes due to their high thrust strength and small diameters.
Capability to manage high torque: Popular in moderately cycled applications and small diameter pipelines, single-acting actuators can manage low torque applications. Applications in the heavy industrial sector require sturdy valves and actuators that can efficiently regulate flow rates. These plumbing systems have significant torque needs, indicating that they consume much energy. As noted previously, the torque supplied by a spring-return actuator is determined by the spring's rigidity. Small double-acting actuators can generate more torque than their single-acting equivalents. Low fluid pressure is required for bidirectional valve operation, reducing the energy needed to pressurize the actuators. Heavy-duty industrial and chemical processing valves commonly use double-acting actuators.
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