Vibration at 5X NDE AND DE V for Centrifugal Pump

WSS

Many styles of centrifugal pumps, can you add more detail

Most of the time, pumps have 2-3 bearings/shaft/impeller/coupling. So if you truly have a 5x peak synchronous to machine running speed and you have 5 vanes on the impeller, then it is vane pass. Bearings will be non-synchronous data

I also see what appears to be harmonics of vane pass, did you change impeller size recently, is there a check valve or valve in general that is stuck or not working properly?

Just by "overhauling" a pump does not mean it can not have vane pass.......

The pump was overhauled as a part of routine maintenance ,there was no indication of vibration prior to overhauling.

LPT was carried out on impeller during overhauling and no damages where observed also when we calibrated the rotor for balancing we found that it was already under tolerance.

This are the main reasons I ruled out vane pass.

This horizontally mounted centrifugal pump acts as a overhung rotor,having a bellow in the suction side and connected to motor using a flexible coupling.Pump has 2 angle contact bearing in DE and one radial bearing in NDE.

I carried out shock pulse test and found bearing pulse to be just under warning range

The pump was overhauled as a part of routine maintenance ,there was no indication of vibration prior to overhauling. ok, then it should not be vibrating now right....then something changed...is the pump running backwards, just because the valve handle moved does not mean the internals moved, did something fall/collapse and block pump inlet, are flows and pressure normal, did you change impeller size

I assume "calibrated" means balanced the impeller

This are the main reasons I ruled out vane pass. I agree that as long as you did not change impeller size or design then there should not be vane pass, but if the suction or discharge of your pump is partially blocked you can see vane pass, it is created by hydraulic issues with pump performance. Like not enough liquid on suction side or restricted piping on discharge due to dirt buildup

This horizontally mounted centrifugal pump acts as a overhung rotor,having a bellow in the suction side and connected to motor using a flexible coupling.Pump has 2 angle contact bearing in DE and one radial bearing in NDE.

I carried out shock pulse test and found bearing pulse to be just under warning range shock pulse does not account for vane pass or 1x or 2x, it uses the ultrasonic range to identify faults at an early stage, very sensitive to flow/cavitation/lubrication defects

https://en.wikipedia.org/wiki/Shock_Pulse_Method

Dave

Thank you guys for your reply.The pump is at site and we are service contractors.So is it safe to conclude that occurrence of vibration is not due to any wrong procedure in overhauling (ie. balancing,Replaced bearings and gasket,mech seal test)? 

Please note we had changed the bearings too.

Greetings team

 

Very Interesting case. only 5X dominating. No problems noticed in spectrum. All unique components are in good condition.  

3.84 mm/s at 5X is still in normal condition. However, the cause of 5X dominant can appear due to flow conditions like impeller stall. 

 

Check the pump suction and delivery valves, system flow conditions (full flow or throttled flow) Load on motor etc.,

Pleased to see such isolated case.

 

regards

Chary

 

GREETINGS

WELL NOTED. 

THANKS FOR YOUR FEEDBACK.

PLEASE FOLLOW THIS METHOD AND TRY HOW YOUR VIBRATIONS ARE INDICATING.

1. CLOSE DISCHARGE VALVE AND START THE PUMP AFTER FEW SECONDS AT FULL SPEED AT MAXIMUM PRESSURE MEASURE THE VIBRATION SLOWLY OPEN DISCHARGE VALVE AND MEASURE THE VIBRATION. 

IF FLOW INCREASING TIME VIBRATION RISING IT IS RELATED TO FLOW SURGES CAUSING THE VIBRATION. IF STEADY AT EVERY DISCHARGE VALVE POSITION THEN THE VIBRATION IS NOT FLOW RELATED.

ALSO TAKE RUN UP AND COAST DOWN AND RECORD RESONANCE FREQUENCY.

BUMP TEST ALSO HELPS BUT RUN UP/COAST DOWN IS BETTER.

APPRECIATE YOUR FEEDBACK.

 

REGARDS

CHARY

 

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