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A vapor recovery unit that has become louder is usually reporting a change somewhere else. Noise in these units is generated mainly by the vacuum pump or blower and by the flow of vapor through the train, so a change in sound generally means a change in how the machine is being operated or what it is being asked to move. Working through the train from the inlet to the machine locates the cause faster than starting at the machine.
Start with the inlet
If liquid is reaching the pump, it will sound different. Entrained droplets produce a rougher note and can cause cavitation-like behaviour as they pass through the machine. The first check is therefore the knock-out drum: level, drainage, and whether the demister is passing liquid. A drum that is sitting high or draining slowly is a common and easily corrected cause of a new noise.
Then check the path through the train
| Check point | Possible cause of new noise | What to do |
|---|---|---|
| Knock-out drum | Liquid reaching the pump | Check level and drainage first |
| Filters and strainers | Loading raising pressure difference | Compare pressure drop with normal |
| Condenser | Frost or fouling changing flow | Check outlet temperature and pressure drop |
| Pipework and supports | Vibration transmitted or loosened | Check fixings and contact points |
| Machine mounting | Isolation deteriorated | Inspect mounts and base condition |
| Machine itself | Wear, seal or internal damage | Escalate to a qualified technician |
Separating flow noise from machine noise
Flow noise varies with throughput: it changes when the unit’s load changes and tends to fall away as the train settles. Machine noise tends to be steady and present whenever the machine runs, regardless of what the rest of the train is doing. Listening at a point where the unit is not loading, or briefly at reduced duty, quickly distinguishes the two, and that distinction decides whether the response is a process adjustment or a maintenance action.
Working the checks in order
- Note when the noise started and whether it varies with load;
- Check knock-out drum level and confirm drainage is working;
- Compare filter and strainer pressure drop with the normal value;
- Check condenser outlet temperature and pressure drop;
- Inspect pipework fixings, supports and machine mounts for looseness;
- If the noise is steady machine noise, escalate before running the unit further.
Frequently asked questions
Can a louder unit still be working normally?
It can, but a change in sound is information. Even where performance looks acceptable, a new noise is worth investigating before it develops into something that affects recovery or damages the machine.
Is cavitation likely in these units?
It can occur where the machine is being asked for a pressure difference it cannot comfortably achieve, or where liquid is present in the suction stream. Both are worth ruling out early because both are damaging.
When should the unit be stopped?
If the noise is accompanied by vibration, a rise in machine temperature, or evidence of liquid reaching the machine, stopping and inspecting is the safer choice. A short planned stop is cheaper than an unplanned failure.
Luoyang Wohong Petrochemical Equipment Co., Ltd. designs and manufactures vapor recovery units, membrane separation skids and condensers for fuel depots, terminals and retail sites. Contact us for duty assessment and equipment selection support.