I am looking for an opinion on some phase and vibration data recently collected on a small Ash Pump. The pumps are a 3 vane cast overhung impeller driven by a 55kW Variable Speed motor. The pump had high motor nde (outboard) vibration levels in the horizontal which trended up over about six months to as high as 17 mm/s before being shut down.

The motor nde has had a history of going high as the pump impeller wears, and experiences much higher vibration than the pump bearings (dog wagging tail effect?). The most recent problem saw the Motor nde quickly trend up during the last stage of it's life.

The attached Phase and vibration appear indicate some misalignment across the coupling and the motor, but the pump has steady phase in all directions. My first thoughts were a resonance problem on the pump but a FRF (hammer test) indicated the pump natural frequency was well away from operating speed. The motor however had a very small response at 18.5 Hz which is close the normal operating speed of around 19 Hz.

While the Frequency Response test helps explain the high vibration on the motor nde being excited by the wearing pump, I still am unsure why the phase on the pump is exactly the same in all directions and does not reflect unbalance.

The pump impeller has been changed and re-aligned and vibration levels are all around 2-3 mm/s on all bearings. Can anyone explain the pump phase readings?

This message has been edited. Last edited by: Nick Lee,