Guide to Choosing Between Doubleacting and Springreturn Valve Actuators

Many engineers face the dilemma of selecting between double-acting and spring-return actuators for valve automation. While spring-return actuators offer inherent fail-safe features that appeal to safety-conscious professionals, double-acting actuators present advantages in simplicity and cost-effectiveness. However, the decision requires careful consideration of operational requirements and potential risks.

Core Differences: Double-Acting vs. Spring-Return

The fundamental distinction lies in how each actuator responds to power or air supply failure:

• Spring-return actuators (single-acting) use compressed air or electricity to move the valve in one direction. An internal spring returns the valve to its default "fail-safe" position when power is lost. This design is ideal for systems requiring automatic closure or opening during failures to ensure safety or material control.
• Double-acting actuators require power to move valves in both directions. Without a spring mechanism, they maintain their last position during failures ("fail-in-place"). These actuators will only move if sufficient air pressure remains in the system after power loss.

Notably, fail-in-place behavior can be advantageous in certain processes where automatic valve movement might cause overfilling, spills, or material waste. Actuation speed also differs slightly, with spring-return models typically slowing during spring compression while double-acting versions maintain more consistent speed.

Five Critical Selection Factors

1. Size and Space Requirements

Spring-return actuators generally require more space due to their spring mechanism, while double-acting models offer more compact designs. This makes double-acting actuators preferable for mobile equipment or space-constrained installations.

2. Cost Considerations

Double-acting actuators typically have lower upfront costs and reduced maintenance needs. Spring-return models carry higher initial expenses and may require spring replacement over time, especially in high-cycle applications.

3. Fail-Safe Requirements

Spring-return actuators are mandatory when uncontrolled valve positions could endanger personnel, equipment, or the environment. Double-acting models are suitable when maintaining the last position is acceptable or preferred.

4. Air Consumption

Double-acting actuators consume approximately twice the air of spring-return models since they require power for both opening and closing movements. This factor becomes significant in high-cycle systems or facilities with limited air supply.

5. Operational Lifetime

Spring fatigue can eventually affect spring-return actuator performance, potentially slowing return strokes or causing timing inconsistencies. Preventive maintenance and monitoring systems can help mitigate these effects.

Application-Specific Recommendations

Spring-return actuators excel in:

• Safety-critical systems (chemical feeds, batch processes)
• Gravity-fed or municipal water systems where uncontrolled flow poses risks
• Environments requiring automatic shutdown to prevent contamination or damage

Double-acting actuators are preferable for:

• Space-constrained installations
• Processes where maintaining valve position prevents material waste
• Cost-sensitive projects without strict fail-safe requirements

The choice ultimately depends on specific operational requirements, with spring-return actuators representing the safety-first option and double-acting models offering practical advantages when fail-safe operation isn't mandatory.