Balancing, wear and troubleshooting
Be the pump doctor: balance a shaking impeller and diagnose the usual problems.
⏱ 7 min
- Everyday comparisonStep 1 of 6
The wobbling washing machine
When all the wet towels end up on one side of the drum, the washing machine thumps and walks across the floor during the spin.
An impeller that is heavier on one side does the same thing — at thousands of RPM. That is .
- Try itStep 2 of 6
Balance the impeller
This impeller has a heavy spot from the casting. Add a correction weight and choose where to put it. Watch the vibration trace and the shaking force.
The animation is slowed down enormously — the real one spins at 2900 RPM.
Challenge: Get the leftover unbalance below 1 g. Where did the weight have to go, compared with the heavy spot?
- ExplainedStep 3 of 6
Why a few grams matter
The shaking force grows with the square of the speed. At 2900 RPM, just 12 g at the rim of a 200 mm impeller pulls the shaft round with about 110 newtons — like hanging an 11 kg weight off the bearings, spinning 48 times a second.
In the factory, a balancing machine finds the heavy spot and a little metal is ground off there. That is .
- ExplainedStep 4 of 6
The pump doctor’s checklist
No water at all: not primed, air leaking into the suction pipe, a closed valve, or the motor turning the wrong way (a backward-spinning impeller still pumps a little, which fools people).
Too little flow or head: worn wear rings, a partly clogged impeller, speed too low, or the system needs more head than expected.
Gravel noise: cavitation — check the NPSH. Vibration: unbalance, of motor and pump, worn , or running far from the BEP.
- ExplainedStep 5 of 6
Wear happens
Over the years the wear-ring gaps grow, vanes erode, and the wears. Performance creeps down and power stays up.
Good maintenance compares the pump’s measured flow, head and power with its original curve. When the gap between them grows, it’s time for new wear rings — much cheaper than a new pump.
- The impeller connectionStep 6 of 6
Listen to your pump
Vibration sensors and power meters now let pumps report their own health. A change in vibration or in power for the same flow is often the first warning sign of trouble — long before anything breaks.
📌 Remember this
A few grams of unbalance create large forces at high speed, so impellers are balanced. Most pump problems trace back to priming and air, wear, cavitation, misalignment or running far from the BEP.