Phase Analysis: Step By Step Procedure

[N4907]

Hi

I am looking to get a step by step procedure to carry out phase analysis for a basic machine train (say Direct coupled motor driven pump) operating at 3000 rpm.
The spectrum is showing harmonic peaks gradgually reducing in amplitude (i. e. 1X > 2X > 3X and so on...). There is no indication of bearing deterioration at this stage although overall vibration value has suddenly increased from 2.00 mm/s to 15 mm/s .

Help me .


N4907

 

[electricpete]

I'm not a hands-on vib guy so I can't give you step-by-step procedures.

But I know it will be helpful for you to identify what kind of analyser do you have? Also do you have strobotach and access to a point on shaft with a mark?

 

[dgallagher]

Looks like Mechanical Looseness is indicated by the strong running speed harmonics.

- Vibration may be directional, compare vertical and horizontal measurements. In horizontally mounted machines, the 1xRPM component often is greater in Vertical direction than Horizontal when clearances open up.

- a high 3xRPM component can indicate a bearing slipping on the shaft while a high 4xRPM can indicate a bearing loose in its housing

- confirm low or normal axial vibration

- check for noisy or impulsive waveform

 

[vanstoja]

Info provided is sparce. How many nX harmonics and how wide the F-A spectrum? You can fill a 0-2KHz spectrum with nX harmoniccs if you have a serious metal to metal rub. A soft rub (eg, rubber O-ring in the motor maggap) can put a limited number of nX harmonic focused around the principal response frequency of the rubbing components. If a centrifugal pump, how many impeller blades? You could have an impulsive, distorted impeller blade passing waveform producing lowside sidebands that combine with an impulsive rotational waveform to fill the spectrum with nX peaks from 1X to beyond the blade passing fundamental. I'd say that with a 7.5 increase in vibration level you've got a problem! Vanstoja