Vibration measurement decline measurement pumps

A client was planning to replace 3 pumps. After installing the first pump a measurement was carried out in different process conditions. The aim was to check if the pump could be used in the stated specifications.

Opzet meting: 

6 sensors were attached to the machine: 

  • Motor non-clutch side -> ch1 
  • Motor clutch side -> ch2 
  • Motor axial -> ch3 
  • Pump clutch side -> ch4 
  • Pump non-clutch side -> ch5 
  • Pump impeller housing -> ch6
Vibration measurement pumps

A trend was composed on the basis of these 6 sensors. This way we see the transitional phase between the different operating conditions. As soon as a stable point was reached, raw data was captured in order to enable an accurate analysis of these conditions.

Findings:

The following graph shows the first part of the trending.

Vibration measurement trending graph
a) Background vibrations

Before starting up the machine a first measurement was conducted to determine the background vibrations. We notice a very low vibration level. With such values damage during standstill can be ruled out.

b) During start-up

 we notice a slight increase in vibrations. This is a normal phenomenon. Within one minute the vibrations have stabilized. This increase is mainly caused by the start of whirling in the medium. The graph indicates the measuring points where accurate data are recorded. Each indication is explained briefly.
Start-up of the machine

Vibration measurement pump measurement points on graph
1) Process condition 1

The following graph shows the process condition. At this moment we notice very stable vibrations. Below are the spectral analyses.

Vibration measurement pumps spectral analysis graph

At 13h17 the pump experienced a few outages and started up again every time. This explains the trending for the varying signal.

2) Process condition 2

The following graph shows the process condition. At this moment we notice very stable vibrations. There is hardly any difference with condition 1. Below are the spectral analyses.

Vibration measurement pumps proces conditions spectral analysis graph
3) Process condition 3

The following graph shows the process condition. At this moment we notice a slight increase of vibrations compared to before, especially at the pump. 

Below are the spectral analyses.

Vibration measurement pumps proces conditions spectral analysis graph 3

In this spectral analysis there is hardly any difference with the previous measurement. The difference between the two measurements is noticeable between 2200Hz en 4000Hz. This is a high frequency range and is associated with incipient turbulence. This is most clear when we render a 3D graph of the ch5 spectral analyses of all measurements:

Vibration measurement pumps 3D spectral analysis different periods

This point is the lowest the client wishes to use. This vibration image shows only a limited vibration. The variation only indicates that we are nearing the end point of the modulation range. In these process conditions the machine is still perfectly serviceable.

4) Proces condition 4

The flow was slightly increased compared to the previous condition. We notice only a limited decrease of vibrations. The situation is at this point almost identical to the previous one.

Vibration measurement pumps spectral analysis graph 4
5) Process condition 5

In the run-up to this point the trend clearly shows that initially there is a decrease. Again we pass by the previously described working points. When we move towards the maximum flow, there is once again a slight increase in vibrations.

Vibration measurement pumps spectral analysis graph 5

This working point does show the difference in the normal frequency range. We can see that the peaks, with side bands on the rpm, are increasing. We are dealing with an increase in fluid pulsations. At this point we paid particular attention to the forming of cavitation. This could not be measured or heard. 

The following graph shows the spectral analyses of the measuring point at the bottom of the impeller housing. All process conditions are also indicated on this graph.

Vibration measurement pumps spectral analysis with measure points

Overview of the measured process conditions.

Vibration measurement pumps overview process conditions

Conclusion: 

Nowhere in the modulation range do we encounter instable/turbulent conditions. We detect no deviant behaviour of the machine and we can safely say it is mechanically sound. The main difference between the process conditions is due to the behaviour of the medium. 

This measurement allows us to conclude that the other 2 pumps can be replaced in a similar manner.