Could use some advice on this machine. This is a BB5 barrel pump in boiler feed service.... the drive train is actually a 4 machine train.... Boiler feed booster pump is coupled to the motor, the motor (25 Hz) is actually tandem coupled to a fluid drive which then couples to the main boiler feed booster pump (subject).
The fluid drive has a 4:1speed increasing gear set that is always running at 100 Hz... this peak transfers across the coupling into the main BFP (very low amplitude) and is always present.... this peak itself in the spectrum is not resonance.
The problem with this pump is the PIV vibration amplitudes (around .4 ips when I collected data)....the main BFP will usually runs around 5445 rpm (will vary speed depending on unit load), and as they approach this speed of 5445 rpm the vibration at the PIV location increases considerably (which had me thinking about a potential resonance).
*Note - this site only records DCS vibration from the DE in the PIV location... there is no sensor on the PIH location that they can see*
I have attached a PDF with all of my impact test results as well as two spectrums from the PIH location and the PIV location, and both the PIH/PIV spectrums in log scale.
The vibration at the inboard bearing housing is not highly directional.... PIV was .4 ips while the PIH was around .34 ips. The vertical direction of this bearing housing is very stiff... there is a very short/stiff 4" oil drain piping beneath it, which surprises me that this direction would have the highest vibration amplitudes.
In doing my impact tests, you can see there is a peak with a substantial phase shift right around 100 HZ. You can see this peak also in the PIH location as well.... looking even further away at the POH location, you can see a hint of the peak with a clear phase shift.... not in the POV direction though.
My initial thinking is that this resonance is very heavily damped, however it may be contributing to the amplitudes in the PIV direction. Do you have the same opinion based on the provided data? I don't believe this is the "sole problem" behind the 1x peak, but I believe it is increasing the amplitudes to a certain degree.
Operating speed is 90.75 Hz, while this peak is at around 100 Hz. That is a separation of around 10%.
Cross channel phase from the PIH to PIV locations showed a phase shift of 312 degrees, so I don't think there is much influence from imbalance.
Cross channel phase from the POH to POV location show a phase shift of 123 degrees, which makes me think there isn't a significant influence from imbalance on this end either.
There are 3 other pumps running in this building that are of the same design and speed.... I was concerned that the 100 Hz NF I think I am seeing is background noise, however given the phase shift... I am thinking it is a true NF. Coherence at this peak during the impact testing was .948. Looking at the spectrums in log scale, it does look like this resonance is present.... do you agree with this?
An additional question of mine is this.... you can clearly see the non-resonant 100 Hz peak in the spectrum... as previously mentioned this transfers across the coupling into the main BFP... this peak is very low in amplitude... if this 100 Hz NF peak I am looking at is in fact resonant, why would the 100 Hz peak that transfers from the fluid drive not be excited (ie; higher amplitude)? Technically, there is no excitation for this peak in the pump... it comes from the fluid drive. Not sure about this?
Could you please review and let me know what you think? Would appreciate any and all help.... just want to make sure I am not looking "to hard" for resonance and trying to make something out of nothing.