Shaft run out on vibration


Can shaft run out at the shaft end have an effect on the vibration?

Online shaft vibration probes (proximity probes) are located at the bearing area on the shaft and if there is no run out at the bearing area but only at the shaft end does it still contribute to shaft vibration?

As I understand, the proximity probes will see the bearing seating area on the shaft and if there is no run out at that location, there shouldn't be any vibration related to run out. Am I correct?




Original Post

Dear Nagesh

Proximity probes look at probe track area, kindly clear the type of rotor(compressor/turbine) and whether the runout you are talking about is simply mechanical or combination of mechanical and electrical.

Total indicated runout is a combination of mechanical and electrical runout commonly known as glitch.

Now coming to the second part of the question if the shaft end having runout can cause a problem if coupled to a main oil pump, governor, or it lies in the loaded part of the bearing.

Also please confirm the runout readings at the center portion of the shaft.



Your question is somewhat confusing.  Having said that let me explain that a proximity probe simply sees the change in gap between the probe tip and the materiel passing under that tip. 

Let's take a scenario where the vibration is "zero" but the shaft has runout of 0.2 mm.  The probe would read 0.2 mm. 

Let's take another scenario where the vibration is 0.2 mm and the runout is "zero", an absolutely perfect shaft with respect to runout.  The probe would read 0.2 mm.

In the real world you encounter situations where runout of 0.2 mm and vibration of 0.2 mm may also be equal or near equal but opposite in phase, in which case the probe can read "zero".  But the 0.2 mm of dynamic motion can destroy the machine.

These are the reasons why a once-per-turn reference (Keyphasor) is desired so that you have the ability to vectorially subtract the effect of runout and establish dynamic motion. 


I agree that the question is incomplete.  Monitoring eccentricity (runout) away from the bearing is done on some machines.  This can be an indication of mass eccentricity due to bow.  

It may be  philosophical as to whether runout at the end of the shaft causes problems or whether its measurement detects issues.  Mechanical runout at the end of a shaft that has a mass or coupling could be a big problem.  Is there a concrete example of what you are interested in?

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