Hello.
Maybe you would be able to help me to find the source of vibrations that we've got on na motor that is installed on a vertical pump. High level of vibration is only in one direction (perpendicularly to discharge pipe), highest on NDE. Motor is working with VFD. Motor type: 1LE5603-3BD23-4GR3-Z 315kW 400V 744 rpm. VFD type: SINAMICS G120P 6SL3710-1PE36-6AA0-Z 355kW 400V. Pump maximum speed is 684 rpm.
The casue of high vibrations is peak at 25,75(@604rpm)-24,94Hz(@656rpm). As you can see it's not a multiple of 1x harmonic and with increasing rotation speed the frequency is decreasing. Below 529 rpm peak at ~26Hz is almost invisible. Above 600 rpm vibartion level is inadmissible.
I was thinking that maybe the cause is beating but 1x harmonics are not in the frequency range 24-26Hz. Is it possible that it is related to the VFD? What is your opinion?
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More details please,
Old/new installation/recent repairs/piping changes
Pump flow and pressure correct
Speed related vibration can be a natural frequency being excited, especially when vibration is not related to run speed and is directional.
How is the grout condition under the pump, motor interface to the top of the pump, have you checked all hold down bolts for soft foot/pipe strain
Page 2 of your report shows sidebands at the base of the 25hz peak, what is the spacing of these side bands.
Vibration present with pump off, I assume taken in direction with the highest vibration? This peak is below running speed, this can indicate a flow problem.
The pump will have a curve associated with its performance. You need to plot the flow/pressure/motor amps at different operating speeds and verify the pump is operating on its curve. Broken valves, restricted/partially blocked pump inlet, low water levels on suction all can contribute to vibration.
A bump test inline with discharge and perpendicular to discharge will identify if there is a natural frequency in the 25hz range
Dave
@Registered Member posted:More details please,
Old/new installation/recent repairs/piping changes
Pump flow and pressure correct
Thank you Dave for the reply.
New installation, flow and pressure correct.
@Registered Member posted:Vibration present with pump off, I assume taken in direction with the highest vibration? This peak is below running speed, this can indicate a flow problem.
Yes, taken in direction with the highest vibration.
@Registered Member posted:Page 2 of your report shows sidebands at the base of the 25hz peak, what is the spacing of these side bands.
0,438 Hz
@Registered Member posted:How is the grout condition under the pump, motor interface to the top of the pump, have you checked all hold down bolts for soft foot/pipe strain
Everything is okay.
@Registered Member posted:Speed related vibration can be a natural frequency being excited, especially when vibration is not related to run speed and is directional.
Page 2 of your report shows sidebands at the base of the 25hz peak, what is the spacing of these side bands.
A bump test inline with discharge and perpendicular to discharge will identify if there is a natural frequency in the 25hz range
Sidebands are at 0,438 Hz from the peak.
I'm attaching results of the bump test that I performed. As you can see, there is something in frequency range 20-27Hz but it's not dominant. There seems to be an excitation in this frequency range but it's between 2nd and 3rd harmonic of 1x so what causes the excitation?
Attachments
Files (1)
Bump test is to confirm whether there is a frequency peak present near operating speed, amplitude does not matter. Can you explain how this bump test was acquired? There could be a torsional/twisting mode of the pump shaft or some component of your pump.
Sharp piping bends, pipe reducers 10" to 6", air trapped at a high spot, improper header configuration, improper NPSHa, air in liquid being pumped, cavitation, failed or improperly installed check/hand valves all can create flow related vibration. If you were to blow across the top of a beer bottle, it takes just the right angle and wind pressure to make it sing, does the noise sound similar to that?
Can you provide images of your installation
I have to assume there is more than 1 pump, system configuration, explain how they are to operate
Do you see/feel any certain part of the machine vibrating more than other parts? Like the motor shakes but not the pump, does piping shake? Vibration levels on the pump base plate should be less than .01 in/sec/pk if grout and baseplate design is good. Is the sound present in one location of the machine and not others?
https://www.youtube.com/watch?v=ltWFzjRNBaE
The link shows the effect a suction bell to improve pump performance, same holds true for vertical pumps, you have to have the correct configuration or you will have issues
Dave
I have some doubts about the bump test suitability. You should make it on the motor NDE, not on the baseplate as it is written above your spectrum. You have a peak at about 2 Hz, which couldn't be real. Such type of vertical pumps usually have natural frequency at about 25-35 Hz.
THe Bump Test is not good. The impact (hammer) and response (acceleometer) should be at top of motor (NDE) in the horizontal plane and in two orthogonal directions corresponding to direction with highest vibration and lowest vibration. If you are not using an impact hammer with load cell, then measure background vibrations first. More instructions can be provided.
I'm laughing at all the comments about the bump test not (more or less) being done correctly. I'm laughing because of the number of instances where I didn't have all the fancy equipment and somehow was able to learn something by using a single accelerometer, peak hold on an FFT, and a 2 x 4 to bang on the machine.
I like the timber approach if you are not doing a real modal. This can put real energy into the lower modes. I used to use a little larger cross section if I could find it. Use the end. Swing it like a bat and see how that works for you, not my preference.
John my experience with the equipment you referenced was for the most part very enlightening.
@Registered Member posted:Bump test is to confirm whether there is a frequency peak present near operating speed, amplitude does not matter. Can you explain how this bump test was acquired? There could be a torsional/twisting mode of the pump shaft or some component of your pump.
Sharp piping bends, pipe reducers 10" to 6", air trapped at a high spot, improper header configuration, improper NPSHa, air in liquid being pumped, cavitation, failed or improperly installed check/hand valves all can create flow related vibration. If you were to blow across the top of a beer bottle, it takes just the right angle and wind pressure to make it sing, does the noise sound similar to that?
Can you provide images of your installation
I have to assume there is more than 1 pump, system configuration, explain how they are to operate
Do you see/feel any certain part of the machine vibrating more than other parts? Like the motor shakes but not the pump, does piping shake? Vibration levels on the pump base plate should be less than .01 in/sec/pk if grout and baseplate design is good. Is the sound present in one location of the machine and not others?
https://www.youtube.com/watch?v=ltWFzjRNBaE
The link shows the effect a suction bell to improve pump performance, same holds true for vertical pumps, you have to have the correct configuration or you will have issues
Dave
Hello Mr Dave.
Thankyou for share many information.
In my site have same problem withthe author publish. The Vertical Pump with install side by side. Amplitude was high in NDE Motor Vertical Axes, The Spectrum show 1x Order
Motor speed : 1485 rpm