Vertical Motor ?
Vertical Motor ?
(OP)
Please share your experience on what can cause an up thrust on a vertical small deep well pump motor. Our facility rebuilt a 75hp 2-pole vertical motor only, a couple months ago and it was pulled for high vibration on the top end (thrust bearing end) After close inspection the lower guide bearing shows signs inside the outer race, a wear grove as if the bearing was operating in an up thrust position for an extended length of time. End play adjustments are at specifications of .008
Note: The lower guide bearing also shows signs of heat and lubrication was starting to breakdown. The top end looks fine?
Thanks in advance!
motorhead
Note: The lower guide bearing also shows signs of heat and lubrication was starting to breakdown. The top end looks fine?
Thanks in advance!
motorhead





RE: Vertical Motor ?
1. The stator iron and rotor iron are not properly aligned giving a magnetic upthrust force proportional to the offset distance between stator and rotor magnetic centers and to some power function of airgap electromagnetic flux density.
2. There is a differential pressure across the rotor core due to a change in pressure distribution of the motor cooling fluid. Did you change cooling fan blade numbers or diameters or introduce screens or other blockages in the coolant flowpath?
3. The pump impeller discharge centerline has been moved upward, reducing impeller hub to casing clearance which increases backside leakage flow velocity, reduces static pressure and increases axial hydraulic upthrust. If impeller displacement prevents backside hub leakage flow and increases front shroudside leakage flow and pressure level then front shroud will have higher uptrust force.
4. Post motor rebuild operating flow/head conditions have changed. Axial hydraulic downthrust due to impeller eye pressure imbalance varies with the square of running speed (it's a function of head) so lower running speed will increase hydraulic upthrust over the entire operating flow range. If head generation in hub to shroud streamtubes varies with flowrate then thrust reversal may occur before head runout at high flowrates and you'll have axial hydraulic upthrust. Same thing can happen at very low flows if impeller flow stalls, becomes unstable giving a drooping head characteristic toward shutoff.
5. All the other things I haven't thought of.
RE: Vertical Motor ?
RE: Vertical Motor ?
http://www.geocities.com/worrapol_tpe/mvn.html
http://www.china-tianyi-pump.com/SerialInfo.asp?serialid=38
etc. for more info
Also, please provide more info about the type of pump and motor you have.
The motor power supply quality could be checked for harmonics and common mode currents.
RE: Vertical Motor ?
Thanks for the good tips.
Kind Regards
motorhead
RE: Vertical Motor ?
RE: Vertical Motor ?
The motor was completely recondition again and put back in to service. It's nice to work with an honest customer, once communicated of the signs of up thrust on the lower guide bearing the customer inspected the pump and found the problem with the impeller and our facility did not have to EAT this repair.
RE: Vertical Motor ?
RE: Vertical Motor ?
Why take any chances, it would be more cost effective to replace both bearings then take a chance and have down time again because maybe the top bearing has some internal damage from operating in an up thrust positon also, there is no signs of this, but why take the chance.
RE: Vertical Motor ?
Sounds like the varnish was overkill but the customer is always right (right?)
RE: Vertical Motor ?
RE: Vertical Motor ?
RE: Vertical Motor ?