Impeller Wear
A worn impeller reduces pump performance and efficiency. Learn the causes of impeller wear, how to detect it, and when to replace or refurbish.
Causes of Impeller Wear
- Abrasive particles: Sand, grit, or other solids in the pumped fluid act as an abrasive, wearing down the impeller vanes and casing. Common in mining, dredging, and well water applications.
- Cavitation: Vapour bubble collapse near the impeller surface causes localised pitting and erosion. Typically on the suction side of the vanes.
- Corrosion: Chemical attack by the pumped fluid. Common with acidic or alkaline liquids. Impeller material must be compatible with the fluid.
- Recirculation: Low-flow recirculation causes pitting on the impeller inlet (suction recirculation) or outlet (discharge recirculation) vanes.
- Erosion: High-velocity fluid, especially at the impeller outer diameter, gradually wears the vane tips and casing.
Symptoms of Impeller Wear
- Reduced flow: The pump cannot deliver the flow rate shown on its performance curve. Worn vanes are less effective at moving fluid.
- Reduced head: The pump cannot reach the discharge pressure it used to. The shut-off head is lower than the pump curve indicates.
- Increased vibration: An eroded or imbalanced impeller causes vibration. Not always present, but a useful indicator if other symptoms are present.
- Higher power consumption: If the impeller is corroded (rough surface), friction increases and the pump uses more power for the same flow.
Detection and Measurement
The most reliable way to check impeller condition is to compare actual pump performance to the manufacturer's curve. Measure flow rate and discharge pressure at the operating point. If the pump delivers significantly less flow or head than the curve predicts, the impeller is likely worn.
For a definitive check, dismantle the pump and visually inspect the impeller. Measure vane thickness and compare to original dimensions. Look for pitting, erosion, and corrosion.
| Wear Level | Performance Impact | Action |
|---|---|---|
| Minor (less than 1mm) | ~5% capacity loss | Monitor. Plan refurbishment at next scheduled maintenance |
| Moderate (1 to 2mm) | ~10 to 15% capacity loss | Replace or refurbish impeller soon |
| Severe (more than 2mm) | 20%+ capacity loss | Replace immediately. Pump is wasting energy |
| Pitting from cavitation | Variable | Fix root cause before replacing impeller |
Wear rings vs impeller replacement
Before replacing the impeller, check the wear rings. Worn wear rings cause internal recirculation (fluid leaks from discharge back to suction), reducing performance. Replacing wear rings is much cheaper than replacing the impeller and may restore most of the lost performance.
Tip: Trend pump performance over time. Record flow rate, discharge pressure, and motor current at a fixed operating point. A gradual decline in performance indicates progressive wear. When performance drops 10 to 15% below baseline, schedule impeller or wear ring replacement.