The Exhaust That Was Too Loud
We ran a pneumatic cylinder (fast cycle, article 171). The exhaust (from the valve, article 90) was loud — 85 dB(A). The operator complained (hearing fatigue). The problem: no muffler (silencer) on the exhaust. The valve exhausts air (loud puff) on every cycle. We added a muffler (silencer, article 75) on the valve’s exhaust ports. The noise dropped to 70 dB(A). The operator was comfortable. The mistake was not muffling the exhaust.
Pneumatic silencer (muffler) sound level reduces the exhaust noise. This article covers the selection.
Why the Exhaust Is Loud
A pneumatic valve (article 90) exhausts air (when the cylinder switches). The air (at 6 bar) rushes out (a fast expansion). That’s loud (85–90 dB(A)). For a fast cycle (article 171), the exhaust repeats every cycle (the noise is continuous).
The Silencer (Muffler)
A silencer (muffler) screws onto the valve’s exhaust port. It’s a porous element (sintered plastic, or bronze) that the air passes through. The element breaks up the noise (the sound waves cancel). The exhaust is quieter (70 dB(A) or less). But it adds a little back pressure (the air has to push through the element). For a fast cylinder (article 171), don’t over-muffle (the back pressure slows the cylinder). Use a silencer with enough flow (low restriction).
Step 1: Muffler Sizing (Flow)
A muffler has a flow rating (NL/min). For a fast cylinder (article 171), the exhaust flow is high (the same as the supply flow). Pick a muffler that passes the exhaust flow (not the smallest one). A small muffler (high back pressure) slows the cylinder. A big muffler (low back pressure) is quiet and fast.
The muffler rule: Add a muffler on every valve exhaust. The exhaust that was too loud had no muffler. Use a muffler rated for the exhaust flow (not too small). It drops the noise to 70 dB(A). For a fast cylinder (article 171), pick a low-restriction muffler.
Step 2: OSHA Noise Limit (Article 75)
OSHA (article 75) limits the noise to 85 dB(A) (over 8 hours). A muffled exhaust (70 dB(A)) is under. An unmuffled exhaust (85 dB(A)) is at the limit. For a noisy machine, add mufflers (and isolate, article 162). The operator doesn’t need hearing protection (under 85 dB(A)).
Step 3: Muffler Types
- Sintered plastic: Cheap. General. 70 dB(A).
- Sintered bronze: Better flow (less back pressure). For fast cylinders. 72 dB(A).
- High-flow (large): For a big valve (high flow). Very quiet (68 dB(A)).
Step 4: Cleaning (Article 147)
The muffler clogs (with oil, dust, article 147). The back pressure rises (the cylinder slows). Clean (or replace) the muffler every 6 months. A clogged muffler is worse than no muffler (high back pressure).
| Exhaust | Noise |
|---|---|
| No muffler | 85–90 dB(A) |
| Sintered plastic muffler | 70 dB(A) |
| Bronze (high-flow) muffler | 72 dB(A) |
| High-flow large muffler | 68 dB(A) |
A Muffler Checklist
- Is the exhaust loud? (dB(A)?)
- Is there a muffler? (On the valve?)
- Is the muffler rated for the exhaust flow?
- Is the back pressure OK? (Cylinder speed? Article 171?)
- Is the noise under 85 dB(A)? (OSHA? Article 75?)
- Is the muffler clean? (Article 147?)
- Is it replaced? (Clogged?)
- Does the operator complain? (Hearing?)
- Are the other exhausts muffled? (Ejector? Article 173?)
- Is the noise measured? (Sound meter?)
The Bottom Line
Pneumatic silencer sound level drops the exhaust noise. The exhaust that was too loud had no muffler. Add a muffler (rated for the flow). It drops to 70 dB(A) (under OSHA). Clean it (don’t let it clog). The machine that was quiet wasn’t the slowest one — it had mufflers.
