Hi,

I am facing problem in Boiler feed water pump, Pump is driven by turbine. Rated speed 3000 RPM.Coupling Thomas coupling Disk pack. Turbine and pump are having Journal Brgs and thrust Brg is Antifriction Brg.

Recently turbine and pump was o/H, turbine new Brgs and new rotor and dynamically balanced.Pump found everything normal and it was also balanced.Coupling also new.

Turbine solo run performed and vibration was well within the limit less than 1 mm/sec RMS.(all vibration are casing vibration collected using accelerometer with SKF analyzer)

During coupled run vibration was high, as follows

TNDE H/V/A- 8.0/1.2/8.0 MM/SEC rms
TDE H/V/A - 8.5/1.4/6.5 MM/SEC RMS
PDE H/V/A - 7.2/1.6/3.2 MM/SEC RMS
PNDE H/V/A - 7.1/2.1/2.2 MM/SEC RMS

In all locations predominant frequency of 1.38X is present.No 1x is present in the spectrum.

Please share your experience in solving this problem. What is the significance of 1.38x vibration?

Thanks in advance

"No 1X" and "predominant frequency is 1.38X". Are you absolutely certain of your machine speed? How is it being estalished?

John from PA

1.38 sure is a mystery.

Was the vibration during solo run at 1x or at 1.38?

Longshot - put the spectrumn on a log scale to see if that 1.38x is part of a pattern of other peaks that might give a clue.

Longshot - check the machine base to see how high the vibration is there. Might be a base resonance perhaps excited by vibration coming from another machine nearby running at a different speed, or by some broadband excitation, or... ??

Hi,
Thanks for ur reply.

John: RPM confirmed with strobe, Lasetach and tachometer!

Electricpete: No 1.38x during turbine solo run only 1x is present in the spectrum.

No background vibration.

Sounds like there may circulation problems in the pump or lines.

I agree with others.....1.38X is very strange.
Is this peak well-defined and narrow or "broadband" with center at 1.38X (flow related)?
Can you post the FFT and the TW ??

Regards
Jim P