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How Does Impeller Balancing Maintain Pump’s Operation?

November 5, 2019

Just like the wheels on a car, pump impellers require balancing. Sticking with that analogy, a car will shake and shimmy if its four wheels are unbalanced. With that metal or plastic disc spinning eccentrically, well, proportionate pumping action becomes impossible in a centrifugal pump's volute. Flow inefficiency concerns are then likely, as are all kinds of vibrationally induced problems. When push comes to shove, the equipment will cavitate.

Unbalanced Centrifugal Pumps Create Fluid Stresses

Flow inefficiency problems are first up on the spin deficiencies list. With an impeller unbalanced, its pumping chamber discharges less output energy. Noise and vibrations propagate; the shaking works its way forward and back. Fasteners loosen and seals breach. The gaskets near the pump crack and leak. As for the pump and its drive system, the bearings upon which the shaft is mounted will age and fail. Thrust stresses are impacting the bearing races and distorting the bearing rolling elements. Friction is the next domino-like flaw to propagate. Heat stress hits the pump motor and destroys the electrical windings. Even if the electrics inside the pump do somehow manage to function, the turbulence generated inside the fluid chamber could become so bad, so unmanageable, that the whole pumping station triggers a cavitation failure.

Balancing Pump Impellers

Before working this solution into the system, it's a good idea to track down the balance-destroying culprit. Has the impeller received a blow from a solid in the fluid stream? Maybe the pump shaft and its bearings are already damaged? In this case, a replacement motor will be needed to correct the shaft drift. Anyway, after the cause of the defect is identified and addressed, there's still the matter of the imbalanced impeller to address. Small weights are intelligently distributed around the rotating disc to correct the asymmetrical rotation. This action "zeros out" any shaft and spin eccentricities and restores centrifugal equilibrium to the impeller. Aligned correctly once more, full discharge efficiency is restored to the volute.

Cavitation is worse than fluid turbulence. With air entering a pump volute, compressed bubbles wreak havoc on the machinery. That's a worst-case scenario, of course. All the same, even a turbulent fluid stream will produce excessive vibrational waves, which could just weaken a seal. Gaskets aren't immune to such energies, so they crack and leak. Even inside a centrifugal pump, the damage will accumulate. The shaft stress impacts the bearings. To offset such mechanical stresses and fluid turbulences, pump servicing technicians add tiny weights to impellers. These weights are distributed in such a way that they correct spin anomalies and keep the pumping action centrifugally balanced.

Parker Pumps

29B Ormond Rd., East Geelong VIC 3219

Phone: (03) 5229 7443

Email: sales@parkerpumps.com.au

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