Pump maintenance - check the shaft run-out

Shafts get bent. The spinning impeller has unequal loading on in causing the shaft to deflect away from the volute throat. Constant deflection causes weakness and can lead to a permanent offset of the shaft leading to shaft run out. 

Shaft run out is bad for seals. It causes them to flex twice on every revolution of the shaft. At high enough speeds this can cause a vibration in the seal which allows the seal faces to OPEN. BANG failed seal.

So, it is important to  check the shaft of your pump for any damaging shaft deflections by using the Dial Test Indicator (DTI).

Single stage pumps should be checked near the seal running position but multi stage pumps should be checked at suitable intervals along the shaft as well as at the seal running position.

The run out should not exceed 0.002 inches or 0.05 millimetres.