vibration signature - slot filled bearing

[jet1749]

Hi, I'm a vibration amateur, so hopefully someone can advise. The problem was high vibes at 14X running speed on a recently overhauled centrifugal pump. Vibes were at the drive end, which is fitted with a slot filled double row angular contact bearing.
The pump runs at 3000rpm
Vibes were at 14X running speed approx 41,000cpm
14 balls per row in bearing
Filling notch in both the inner and outer rings
BPFO 17372cpm
BPFI 24628cpm
Combined total 42000cpm
Reversing the orientation of the bearing cured the problem, as high suction pressure was believed to have reversed the direction of thrust. The question is, am I correct in my assumption that the BPFO and the BPFI should be added together. Or should I have seen spikes at about 17300 and 25000cpm.
regards
John

 

[electricpete]

I see no reason that a frequency corresponding to BPFO + BPFI should ever be seen in the spectrum.

I would expect the generated vibration to mostly likelly be at frequencies:
j * BPFO +/- k * 1X
m * BPFI +/- n * 1X
where j, k, m, n are integers. 1X is running speed.

I would take a look on a log scale to see if your large peak is part of a family of other peaks (look for sideband series and harmonic series). This may help to piece together the meaning of the frequency that you saw.

Also, high resolution is your friend when trying to figure out an unknown frequenct





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[spciesla]

Is the 14X related to the pump? Perhaps the impeller has 7 vanes and you are seeing 2xVPF. It definitely doesn't sound like a bearing issue at this time.

 

[jet1749]

Thanks for the replies,

The impeller has 5 vanes. Vibes were strongest at the drive end and were actually audible. Reversing the orientation of the double row angular contact bearing cured the problem (thrust forces had been running against the filling slot, but no actual visible damage when the bearing was inspected)

regards
John

 

[Tmoose]

I'm having a hard time imagining that a manufacturer would put, or ever allow, a filling slot or even an oil hole in a ball path. The high stress at the edge of the slot would be murder on the balls and the race.

Was one side of the outer or inner race marked "thrust" or something similar?

 

[jet1749]

Tmoose
Double row angular contact bearings with filling slots are very common. They are a high load capacity bearing but only in one direction. You have to be sure of the direction of thrust in order to take advantage of it. I have changed out this type of bearing on some other pumps, particularly where the direction of thrust can change due to variable operating conditions, or where high suction pressure exist

regards
John