What does a cavitating pump sound like?

The classic description is a rattling, crackling, or "gravel and marbles" noise that seems to come from inside the casing, usually accompanied by vibration and a discharge pressure gauge needle that flickers or hunts instead of holding steady. The noise is the sound of thousands of tiny vapor bubbles collapsing against internal surfaces. It gets louder as the pump is throttled toward a worse operating point and often changes character between low-flow and high-flow conditions, which is itself a diagnostic clue.

How do I know if my cavitation is a suction problem or a recirculation problem?

Suction cavitation almost always shows up as reduced discharge pressure and flow alongside the noise — the pump is genuinely starved of NPSH and cannot make its rated head. Discharge/recirculation cavitation, by contrast, typically occurs while the pump is still developing close to its rated shutoff head, at very low flow relative to its best-efficiency point, with noise and vibration but without the same starvation of suction-side pressure. Plotting the actual duty point against the pump curve, and checking NPSH available against NPSH required, is the reliable way to tell them apart rather than guessing from sound alone.

Will increasing the discharge valve opening fix cavitation?

It depends entirely on which type of cavitation is occurring. If the pump is cavitating because it is running far to the left of its best-efficiency point (low flow, high head, internal recirculation), opening the discharge valve to push more flow through it often helps by moving the operating point back toward BEP. If the pump is cavitating because of insufficient NPSH available on the suction side, opening the discharge valve increases flow demand and can make suction cavitation worse, not better, because it raises the NPSH required by the pump at the same time suction conditions haven't improved.

Can a clogged suction strainer cause cavitation even if the tank level looks fine?

Yes. A partially clogged strainer, foot valve, or suction screen adds friction losses on the suction side that a simple visual check of tank level will not reveal. Those losses subtract directly from the pressure the pump sees at its inlet, which is exactly what NPSH available measures. A tank that looks adequately full can still be delivering far less usable suction head to the pump than it appears to, which is why inspecting the actual suction piping and strainer condition is part of the diagnostic sequence, not an optional step.

Is entrained air the same thing as cavitation?

No, though they produce similar symptoms — noise, vibration, and unstable flow — and are frequently confused in the field. Cavitation is the liquid itself vaporizing because local pressure fell below its vapor pressure; entrained air is actual gas that has worked its way into the suction line, often through a leaking suction-side fitting, a vortexing sump, or a vent that pulls air below a minimum submergence level. The fixes are different: entrained air is solved by sealing suction-side leaks and raising submergence, while true cavitation is solved by managing NPSH margin or the pump's operating point.

Pump Cavitation Troubleshooting: Diagnosing and Fixing the Real Cause

A field troubleshooting guide for cavitating pumps — how to tell suction cavitation apart from discharge/recirculation cavitation from symptoms alone, the diagnostic sequence to confirm which one you have, and the different fixes each requires.

If you found this page while a pump is actively rattling in your plant right now, you probably don't need another explanation of vapor pressure and Bernoulli's principle — you need to know what to check first, and why the same-sounding noise can have two completely different root causes that need two completely different fixes. The underlying physics of why cavitation happens — local pressure dropping below the liquid's vapor pressure, bubbles forming and then collapsing — is covered in detail in the Concept Explainer, Cavitation: How Fast-Moving Water Can Literally Boil at Room Temperature. This guide picks up from there and stays entirely on the practical side: symptom recognition, diagnosis, and the fix.

The Field Symptoms, Quickly

Before splitting cavitation into its two types, it helps to have the shared symptom list in one place, because these are what first get a technician's attention regardless of which type is occurring: