Hello all,

I have vertical pump for drain pit and after overhauling the pump found high vibration levels. we decoupled the pump and conducted vibration test for motor solo run (motor coupling hub installed) and found overall vibration for DE&NDE 9 mm/s Peak in one radial direction and other direction is about 3 mm/s Peak. we suspected balance problem and replaced motor with new one (with the same hub installed), found almost the same result.
vibration readings slightly decreased but still high after replacing the hub with another used one as there's no spare.
Motor data: (3.3 kw motor,2990 rpm with angular contact ball bearing)

the attached spectrum is the latest situation.

what is the problem?should I accept it with 9 mm/s?
I see here a lot of experts and I hope you can help me.

Thanks and regards
Hady

PM-5230_SOLO.doc (86 Kb, 36 downloads) Spectrum

It is high (9mm/sec at no load)More data is required. Was it the same motor installed after overhauling? What were the jobs carried out on the pump, base, motor?
Pl. attach vibration spectrum before overhauling.
Check for any noise in motor bearings. Run the motor in solo after removing cooling fan.
Regards.
Irshad Akhtar

Dear Akhtar
Pump shafts (Goulds Pump model VIT-FF consisting of three shafts with total hight 990cm) were bent and a runout problem with coulping was observed. No work was done to motor during overhaul and first test after overhaul was with the same motor which was replaced after suspecting unbalance(attached spectrum is for new motor which is the current situation)
Bearings and cooling fan are Acquitted as motor is NEW and env. energy showed good bearing.

I suspect motor hub unbalance or resonance

Was the data before overhaul lower? If so, then coupling hub imbalance should not be the problem unless it was balanced in place while connected to the pump and the arrangement is not the same as before removed.

Have you ran the motor without the coupling hub on?

Was the motor completely removed when the pump was overhauled? Was it returned to its original setting and shim pattern. etc.?

Was something altered while the pump was off, like different motor mounting brackets, etc.

The shafts were bent and there was coupling run out. Seems coupling run out (unbalance) caused the sleeve bearings of intermediate shafts to wear away increasing the 3 intermediate shafts run out and finally bend. It appears to be a chronic problem and not introduced after overhaul. How did you correct the coupling run out? Any sort of machining will throw the coupling out of balance (if it is the case with you). Run the motor solo after removing motor coupling.
Regards
Irshad Akhtar

I'd do bump tests in each of the measurement directions, and expect to find a resonant frequency not very far away.

20 years or so ago I was asked to do vibration analysis on some new fairly large US made motors that had high 1X vibration when run solo. They were being tested with no key running on a test bed. A full length half height key secured in the keyway with fiberglass tape and everybody was happy.


When motor and hubs are "balanced" the key/keyway compensation must be well understood.
In the US it used to be that each component was balanced with a full length half height key installed, essentially turning the rotor shaft into solid shafts and hubs into un-keyed hubs. A lot of unfilled keyway can be a pretty big light spot, and excessively long keys with short hubs are a heavy spot. At assembly Decent balance could be achieved by knowing craftsman with a stepped key, or a full height half length key.

DIN called out something different, maybe full length key in the rotor shaft and an empty keyway in the hub, which works, but that could make a LOT of extra work balancing each component.

Not too long ago I saw a spec that allowed either key-simulation method, but a tag needed to be attached explaining which was used.

quote:

Pump shafts (Goulds Pump model VIT-FF consisting of three shafts with total hight 990cm) were bent and a runout problem with coulping was observed.

Do the pumps use threaded couplings to connect the shafts, like Item 14 here ?http://www.lightmypump.com/images/BOWL.jpg

there is an excellent possibility to "bend" the shaft if their end faces do not meet squarely and are forced together by the action of the threaded coupling. A small piece of grit or small ding or otherwise damaged shaft ends WILL cause plenty of runout.

A similar situation results when the impellers and spacers of a multistage pump are loaded on the shaft, and a nut tightened to secure the stacked components. Some ANSI pump and turbine assembly process specs include a hold point whenever a nut is tightened to check and record the runout of the assembly. I'd bet any single item off the dollar menu that problems in the field drove inclusion of that inspection step.

good morning Dan

quote:

Originally posted by Dan Timberlake:
I'd do bump tests in each of the measurement directions, and expect to find a resonant frequency not very far away.

20 years or so ago I was asked to do vibration analysis on some new fairly large US made motors that had high 1X vibration when run solo. They were being tested with no key running on a test bed. A full length half height key secured in the keyway with fiberglass tape and everybody was happy.


When motor and hubs are "balanced" the key/keyway compensation must be well understood.
In the US it used to be that each component was balanced with a full length half height key installed, essentially turning the rotor shaft into solid shafts and hubs into un-keyed hubs. A lot of unfilled keyway can be a pretty big light spot, and excessively long keys with short hubs are a heavy spot. At assembly Decent balance could be achieved by knowing craftsman with a stepped key, or a full height half length key.

I inspected the key/keyway and found the the key is almost covering half length of keyway either the hub or the motor shaft.
I asked workshop to creat half key with full length to check the motor on test bed and if accepted it will be tested onsite.
untill this happen a I'll check motor with the installed key "covering half length of keyway" and I'll inform you the result.
____________________________________________

for the confused collegues please note that "MOTOR IS SOLO RUN ONLY WITH KEY AND HUB WITHOUT COUPLING/PUMP"

This message has been edited. Last edited by: Hadi_abdo,

Gents,

I tested the motor SOLO with Key covering half length of shaft keyway and found overall Radial in one direction is 6.75 mm/s Peak amplified at 1X and the other direction is just 1 mm/s Peak.

I suspected resonance but unfortunatly my equipment did not respond with bump test.

Should I test motor with half key covering all key way? (motor baseplate say it's half key balanced)

Hi Hadi,

Take a look at the case study. this motor was connected to a blower fan. we decoupled the fan and conducted the vib study on the motor solo. i had posted this paper earlier on this board. take a look at the attachment may be you will get some clue.

Cheers,

Madhusudan

vibration_studies_of_motor__solo.pdf (230 Kb, 30 downloads)

quote:

Originally posted by Hadi_abdo:
Hello all,

I have vertical pump for drain pit and after overhauling the pump found high vibration levels. we decoupled the pump and conducted vibration test for motor solo run (motor coupling hub installed) and found overall vibration for DE&NDE 9 mm/s Peak in one radial direction and other direction is about 3 mm/s Peak. we suspected balance problem and replaced motor with new one (with the same hub installed), found almost the same result.
vibration readings slightly decreased but still high after replacing the hub with another used one as there's no spare.
Motor data: (3.3 kw motor,2990 rpm with angular contact ball bearing)

the attached spectrum is the latest situation.

what is the problem?should I accept it with 9 mm/s?
I see here a lot of experts and I hope you can help me.

Thanks and regards
Hady

Three shaft each 990Cm or 1m aprx. So there must be intermediate bearings. What kind of bearings are? thordon/special alloy? For a 3m shaft with intermediate couplings, i dont think minor coupling runout/unbalance could cause high vibrations. I think there must be some thing wrong with pump shaft/bearing assembly. Check out.

quote:

Originally posted by Dinesh Hebbar:
Three shaft each 990Cm or 1m aprx. So there must be intermediate bearings. What kind of bearings are? thordon/special alloy? For a 3m shaft with intermediate couplings, i dont think minor coupling runout/unbalance could cause high vibrations. I think there must be some thing wrong with pump shaft/bearing assembly. Check out.

Please see the attached photo for the pump pump the total pump length from suction bell basement is exactly 982.4 cm

This message has been edited. Last edited by: Hadi_abdo,

thank you all for your assisstance.

The problem was found "wrong key was used with machined unbalanced hub in addition sever impellers wear was found"

A.Hady