I have a 300 HP sleeve bearing motor that the shaft is thrusting axially. The coupling type is flexible disc. The motor is driving a pump. The shop claims that the magnetic center has been set properly and the coupling spacing is right and the motor is level. Any other thoughts?

Thanks,
John J

Has the motor been recently replaced? The pump? What type of pump is it? Are these readings on the motor - opposite drive end axial?
Thanks -

If you are seeing fairly low frequecy axial movement of the motor shaft, it can originate in the pump. Small erratic movement within the pump clearance (typically 10 mils or so) can excite the resonant frequency of the big motor mass attached through the flexible springy coupling (low resonant frequency maybe 0.5-2hz).

We have a set of pump motors (2500 hp horizontal sleeve bearing motors connected by Thomas Shim pak coupling) that experience this. It only occurs when the pump is at low flow. During this condition we always see about 1/8" axial movement of the motor oscillating at about 1hz. When the flow increases, the movement always goes away.

John J

It is not recommended that the rotor hunts and buts up against the sleeve bearing shoulders continuously nor intermittently.

You may want to think about a different type of NON-FLEXIBLE coupling for this application.
Or at least a type of coupling that permits some limited movement for thermal growth, but within the boundaries of the sleeve bearing design.

That is what we at ABB Canada used to recommend to our sleeve bearings motor users some years back.

After making certain that the unit is absolutely level, run the motor uncoupled so as to establish its magnetic center and then, fix it in position and install the coupling accordingly.

Regards,

MarkoLeo

Thanks, Electricpete and MarkoLeo. Good tips. I'll do some more investigating.

John J

If the pump has sleeve brgs then all set-ups are on center - mag cntr, coupling on zero and pump in the cntr of its thrust brgs and the pump needs to be hydraulically balanced w/thrust collar in the middle. Off on any of those factors can cause axial vibration.