Pump Vibration Velocity 2

[GaryL]

We have a pump/motor assembly on a hydraulic power unit installed at a customer's site. The customer has taken velocity readings with an accelerometer of 1.24 in/sec. at 1800 CPM (motor speed) on the pump. According to their Rathbone chart this is extremely high. I am not familiar with this chart and am trying to find some information. It is apparently a &quot;standard&quot; preventive maintenance reference.<br>
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If there is a problem - is unbalance in one of the components a likely source?<br>
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Thanks.

 

[Anthonyr]

1.24 in/sec is an extremly high vibration reading and is in the &quot;Very Rough&quot; range of the General Machinery Vibration Severity Chart. I would suggest taking readings at the support points (bearings) of the pump rotor and compare these to the maximum reading. You may find a high amount of the vibration at one of the supports, which could indicate some looseness at that point.

 

[TimC]

1.24 ips @ 1800 rpm is excessive, is certainly a problem and is an indicator of pending failure. If the frequency of vibration is truely 1800 rpm then the problem is likely to be (in order of liklihood) one or more bearings, a bent shaft or misalignment between the motor and pump. As &quot;Anthonyr&quot; indicated, further monitoring may help to identify the source. However, depending on the length of time the unit has been operating this way, the bearings may need to be replaced anyhow.

 

[VibrationSpecialist]

As stated, the vibration level of 1.24 in/sec (zero to peak or RMS) is considered high and require a shut down. Just one comment, when you state it is an accelerometer that means it is reading acceleration and to obtain it in velocity (in/sec) you used an integrator whether whithin the accelerometor (Velometer) or within the analyzer. If the input signal was integrated in the FFT anlayzer, then you need to check the low frequency cut off. Usually this causes a high amplitude due to integration and not due to forcing function.

 

[GaryL]

We have found that the pump/motor requires better structural support, and are designing the modification. Thanks to all for your help.

 

[brin]

just curious, did you take any additional readings in different locations and orientations? any results? I recommend getting something better than the TK81 for the future, or call in someone who can do spectral analysis with phase @ 1X rotation (relative motion/operating deflection analysis).