Single-Acting Pneumatic Actuator Operation
Basic Principle
A single-acting pneumatic actuator converts compressed air energy into mechanical motion to operate valves, dampers, or other devices, featuring a spring that returns the mechanism to its default position when air pressure is removed.
Core Components & Operation
Its core components include a cylindrical housing, a piston or diaphragm connected to a stem, a spring, and air ports. When compressed air is supplied through the inlet port, it enters one side of the piston/diaphragm, creating pressure that pushes against the spring.
This force overcomes the spring's resistance, moving the stem linearly or rotating the actuator (for quarter-turn models), thus opening or closing the attached device. The pressure required depends on the load and spring stiffness, with typical operating ranges between 20-150 psi.
Fail-Safe Mechanism
When air pressure is released, the spring expands, pushing the piston/diaphragm back to its original position, reversing the stem's movement and resetting the device—typically to a "fail-safe" state (open or closed, depending on spring design).
This fail-safe feature is critical in industries like oil and gas, where sudden air loss must trigger safe shutdowns to prevent hazards.
Key Advantages & Limitations
- Simpler design compared to double-acting actuators
- Lighter weight and requires only one air supply line
- Reduced installation costs
- Force output limited by spring strength and air pressure
- Less suitable for heavy-duty applications needing high torque
- Ideal for fail-safe critical applications
Comparison with Double-Acting Actuators
| Feature | Single-Acting | Double-Acting |
|---|---|---|
| Air Supply Lines | 1 | 2 |
| Spring Return | Yes | No |
| Fail-Safe Capability | Yes | No |
| Force Output | Lower | Higher |
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