The Cylinder That Wouldn’t Reach Speed: Air Supply, Valve, and Exhaust
A Ø50 cylinder on a stamping machine. The customer needed 0.5 m/s extend speed. The cylinder reached 0.2 m/s. The regulator was at 6 bar. The valve was new. The cylinder was new. The problem was the exhaust — the muffler was too restrictive. This is the speed chain: supply, valve, tube, exhaust.
The speed chain
Cylinder speed is limited by the slowest link in the chain:
- Supply pressure: Is the regulator delivering full pressure? If the plant air drops to 4 bar during peak demand, the cylinder runs slow.
- Valve Cv: Is the valve big enough to pass the required flow? A 1/8″ valve on a Ø50 cylinder is undersized.
- Tube size and length: Long, narrow tubing restricts flow. A 4 m run of 6 mm tube kills speed.
- Exhaust restriction: The muffler, flow control, and valve exhaust port all restrict outflow. A clogged muffler is the #1 cause of slow cylinders.
What we found
We checked each link. Supply pressure: 6.2 bar at the FRL. Good. Valve: 1/4″ ports, Cv 0.6. Good for Ø50. Tube: 8 mm, 1 m long. Fine. Exhaust: the muffler on the valve was a sintered bronze type, 1/4″ NPT. We removed it. The cylinder speed jumped to 0.6 m/s. The muffler was restricting the exhaust.
The muffler trade-off
A muffler quiets the exhaust but restricts flow. A standard sintered bronze muffler has a Cv of about 0.3 — half the valve’s Cv. It becomes the bottleneck. For fast cylinders, use a high-flow muffler (Cv 1.0+) or no muffler at all (if noise isn’t an issue).
| Muffler type | Cv | Noise reduction | Use for |
|---|---|---|---|
| Sintered bronze (standard) | 0.3 | 15 dB | Slow cylinders, quiet areas |
| Sintered bronze (high flow) | 0.8 | 10 dB | Fast cylinders |
| Plastic silencer (large) | 1.5 | 20 dB | High-flow valves, quiet |
| No muffler | 2.0+ | 0 dB | Remote installation, noise not an issue |
The flow control
We also checked the flow control. It was set to meter-out on the extend. We opened it fully. The speed improved further. The flow control was partially closed from a previous adjustment. For a fast cylinder, the flow control should be fully open (or removed) unless you need damping at end-of-stroke.
The result
With a high-flow muffler and the flow control open, the cylinder ran at 0.55 m/s. The customer’s requirement was 0.5 m/s. We adjusted the flow control to 1 turn open to bring it to exactly 0.5 m/s. The cylinder reached speed. The exhaust noise was acceptable (the high-flow muffler reduced it by 10 dB).
The speed rule: If a cylinder is slow, check the exhaust first. Remove the muffler and test. If the speed jumps, the muffler was the bottleneck. Then check the valve Cv, tube size, and supply pressure. The muffler is the most overlooked restriction in a pneumatic circuit.
