Pump to Motor Alignment

[Pipoy04]

Good day Gents,

I would like to ask for your technical advice when doing the pump/motor alignment. What causes the motor shaft to be hardly rotated at the start, but when partially rotated, it can be rotated by hand easily? We used sling belt wrap around the shaft with a scaffolding pipe to rotate the shaft motor.

 

[rotw]

Guess its due to breakaway torque (essentially to overcome frictional forces).
You can see it on pump/compressor (required) starting torque curve. The profile is basically/roughly a parabola (fan laws) except at the origin at zero speed where bearing static friction forces must be overcome. Especially for fluid film bearings, its metal to metal contact until hydrodynamic lubrication regime establishes but for that a certain rotational velocity is required to lift off the shaft. I don't know but it could be that your motor has roller bearings but the pump has sleeve bearings where the lubrication fluid is the process fluid.