A pump that suddenly gets louder is telling you something. The trick is working out what – because cavitation, worn bearings and air in the system can sound alike but need very different fixes.
In this guide
Match the sound to the cause
| What you hear | Likely cause | Quick check |
|---|---|---|
| Gravel or marbles rattling in the casing | Cavitation | Low suction pressure? Clogged strainer? Valve partly closed on suction side? |
| Grinding, rumbling or screeching from the motor end | Worn bearings | Bearing housing hot to touch? Noise changes when the pump is coasting down? |
| Gurgling or whooshing | Air in the system | Do air vents work? Is system fill pressure correct? |
| Loud hum, pump won't come up to speed | Electrical – single phasing or capacitor | Check voltage and amps on each phase |
| Knocking or vibration that varies with speed | Misalignment or coupling wear | Check coupling and alignment on base-mounted pumps |
| Chirping at the shaft | Mechanical seal running dry | See seal failure signs |
Cavitation: the pump eating itself
Cavitation happens when pressure at the impeller eye drops so low that the water boils – even when cold – forming vapour bubbles. When they collapse they hammer the impeller, leaving a pitted, sponge-like surface. Left alone, it destroys impellers and seals.
Common causes: a clogged strainer or start-up strainer still in place, a partly closed suction valve, low system fill pressure, high water temperature, or a pump running far to the right of its curve.
Bearing failure
Bearings usually fail from age, water contamination (often from a leaking seal), over-greasing or under-greasing, misalignment or electrical currents from a VFD. Once bearings are noisy, replace them soon – a seized bearing can wreck the shaft and motor.
What to do
- Check the easy things first: strainer, valves, system pressure and air vents.
- Note when the noise happens – at start-up, all the time, or only at high flow.
- Feel the bearing housing (carefully) and look for leaks under the pump.
- If it persists, bring the pump in or send us a short video with sound – it helps more than you'd think.
From the shop: If the noise started right after a new installation or a system flush, check the suction strainer and any start-up strainer first. It's the cheapest fix there is.
FAQ
Is cavitation dangerous?
Not to people, but it steadily destroys the impeller and shortens seal and bearing life.
Can a VFD cause bearing noise?
It can – shaft currents from variable speed drives can damage bearings unless the motor has protection such as a shaft grounding ring.
Related reading
Need a pump or motor looked at?
Bring it in or send us the nameplate details – we supply and service Bell & Gossett and Armstrong equipment. Call (416) 236-2338 or email sales@bramhambros.com.