Cavitation is one of the more damaging things that can happen inside a running pump, and it often develops quietly before it becomes an obvious, expensive problem. Understanding what causes it — and catching the early warning signs — is far cheaper than replacing a cavitation-damaged impeller.
What cavitation is
Cavitation happens when local pressure inside the pump drops low enough for the fluid to form vapor bubbles, which then collapse violently as they move into a higher-pressure region. That collapse releases enough localized energy to erode metal surfaces over time.
Understanding NPSH
Net Positive Suction Head (NPSH) is the key concept here: the pump requires a certain minimum suction-side pressure (NPSH required) to avoid vapor formation, and the system needs to actually deliver that pressure (NPSH available). Cavitation risk rises whenever available suction pressure drops too close to what the pump requires.
Suction conditions
Long suction lines, excessive lift, partially blocked strainers, undersized suction piping, and entrained air can all reduce available suction pressure below what the pump needs — even when the pump itself is in good condition.
Vapor pressure and fluid temperature
Fluid vapor pressure rises with temperature, which narrows the safety margin between available and required NPSH. A pump handling warm fluid is inherently closer to cavitation risk than the same pump handling cooler fluid under otherwise identical conditions.
Warning signs: noise
Cavitation often produces a distinctive rattling or "gravel" sound from inside the pump casing, sometimes described as pumping stones. This noise is one of the clearest early indicators something is wrong on the suction side.
Warning signs: vibration
Increased vibration, particularly if it appears suddenly during operation, often accompanies cavitation as the collapsing bubbles create uneven, irregular forces on the impeller.
Warning signs: reduced performance
A pump losing flow or pressure without any obvious mechanical fault is a common cavitation symptom — the vapor bubbles disrupt the smooth flow path the impeller relies on to build pressure.
Impeller damage
Left unaddressed, cavitation erodes impeller vanes and casing surfaces, visible as pitted, sponge-like damage. This damage is progressive — the rougher the surface becomes, the more it encourages further vapor formation, accelerating wear.
Operating conditions that increase risk
Running a pump beyond its rated flow, throttling on the suction side, or operating with a partially clogged strainer all increase cavitation risk. So does running at higher-than-designed fluid temperatures.
Prevention
Prevention starts with correct pump selection against actual system NPSH available (see our pump selection guide), keeping suction lines short and properly sized, ensuring strainers stay clear, and avoiding operation far outside the pump's designed flow range.
Maintenance implications
Any pump showing cavitation symptoms should be inspected for impeller damage before returning to service, and the root cause on the suction side addressed — otherwise a repaired or replaced impeller will simply wear again under the same conditions.