Single Action Pneumatic Actuator for Valve
Pickup availability could not be loaded
Single-Acting Pneumatic Actuator for Valves — Fail-Safe NC or NO, ISO 5211, 15 Models PACS032 to PACS270
The single-acting pneumatic actuator is the standard automation mechanism for butterfly and ball valves in processes where fail-safe operation is a safety requirement. In case of compressed air supply loss or control signal failure, the internal mechanical spring returns the valve to a predefined position (closed or open) without reliance on active electronic components or power supply. The NC (Normally Closed) configuration closes the valve upon failure — standard for gas, steam, and hazardous fluid services. The NO (Normally Open) configuration opens the valve upon failure — standard for refrigeration, cooling, and processes where flow must be maintained in an emergency.
Available in 15 models from PACS032 to PACS270, covering butterfly and ball valves from small (2") to large (24"+) diameters with direct ISO 5211 mounting without adapters.
Single-acting vs. double-acting — when to specify each
| Criterion | Single-Acting ← This product | Double-Acting |
|---|---|---|
| Fail-safe by mechanical spring | ✅ Yes — spring closes (NC) or opens (NO) upon air failure | ❌ No — remains in last position upon air failure |
| Process safety requirement | ✅ First choice — gas, steam, hazardous fluids | Only when the last position is the safe state |
| Compressed air consumption | Higher — spring opposes resistance to active movement | ✅ Lower — air only in the direction of movement |
| Available operating torque | Lower — spring reduces available torque for valve operation | ✅ Higher — full actuator torque available in both directions |
| Operating speed | Opening and closing at different speeds — spring determines speed in one direction | ✅ Independent speed control in both directions |
| Large valves with high torque | ⚠️ Verify net available torque vs. required valve torque | ✅ First choice for large diameter or high-pressure valves |
| Relative cost | ✅ Similar — same base price, different internal configuration | Similar |
NC vs. NO — define fail-safe position before ordering
The fail-safe position is the most important decision when specifying a single-acting actuator. It must be defined by process risk analysis — not by operational convenience:
- Normally Closed (NC) — fails to close: The spring closes the valve when there is no air. The valve remains open as long as there is air supply and an opening signal. In case of any failure — air loss, compressor failure, air line rupture — the valve automatically closes. First choice for: natural gas and LPG (closure upon failure prevents leakage), hazardous or toxic fluids, reagent dosing where excess is dangerous, block valves in safety systems.
- Normally Open (NO) — fails to open: The spring opens the valve when there is no air. The valve remains closed as long as there is air supply and a closing signal. In case of any failure, the valve automatically opens. First choice for: refrigeration systems where flow must be maintained (closed failure would stop cooling), safety equipment bypasses, emergency cooling systems, processes where interrupting flow is more dangerous than continuing it.
The same physical valve can be configured as NC or NO — the difference is the orientation of the internal spring and the position of the control solenoid. Specify NC or NO when ordering.
Air connection — G ports and working pressure
The recommended air supply pressure is 4 to 7 bar (58 to 100 psi). The actuator's operating torque increases proportionally with the supply pressure — always check the net available torque at the minimum guaranteed air line pressure, not just the maximum pressure.
Selecting the correct model — criteria
To select the correct PACS model for a specific valve:
- Step 1 — Required valve torque: Obtain the maximum operating torque of the valve at the maximum differential process pressure. This data is in each Cematic valve's technical sheet or can be calculated with the technical team.
- Step 2 — Minimum safety factor 1.25×: The selected actuator's torque must be at least 1.25 times the maximum valve torque — check at the minimum guaranteed air line pressure (not the maximum).
- Step 3 — ISO 5211 mounting: Verify that the J or K mounting of the selected model (F03, F05, F07, F10, F12, F14, F16) is compatible with the valve's ISO 5211 mounting.
- Step 4 — NC or NO: Define the fail-safe position of the process and specify the corresponding configuration when ordering.
Cematic performs the correct actuator selection for each valve and process condition combination at no additional cost. Share the valve model, diameter, maximum differential pressure, and required fail-safe position.
Compatible accessories
- Control solenoid 24 VDC / 110 VAC / 220 VAC: For open/close signal from PLC or control system
- Limit switch box: Position confirmation signal (open/closed) to PLC — 2 microswitches or magnetic sensors
- Electro-pneumatic positioner 4–20 mA: For proportional modulating control — positions the valve anywhere between 0° and 90°
- Flow regulators (speed controllers): Independent adjustment of opening and closing speeds
- Air filter regulator: Regulation and filtration of air supply to the actuator — recommended in all cases
Compatible Cematic valves
- ✅ Wafer cast iron butterfly valves — standard series and Series 200
- ✅ Lug type butterfly valves ANSI 150 and DIN PN16
- ✅ High-performance butterfly valves — double eccentric Class 150, 300 and 600
- ✅ PVC wafer butterfly valves
- ✅ SS316 and WCB ball valves — flanged and threaded with ISO 5211
- ✅ PFA anti-corrosive ball valves
- ✅ V-port segmented ball valves
- ✅ Any valve with ISO 5211 mounting compatible with F03 to F16 mounts
For double-acting actuators, see double-acting pneumatic actuator →
For pre-assembled valve + pneumatic actuator sets, see valves with pneumatic actuator →