Pump killers: How to fight the 13 most common centrifugal pump failures? Number 10.

In the series “Pump killers” we investigate the 13 most common causes of centrifugal-pump failure and take a look at the things that can be done to fight these ‘killers’. Every week we will share a new, even bigger, killer. Our goal: to reduce the number of victims by sharing our knowledge.

To get a good understanding of number ten on our list, let's start with a bit of theory and now we also take a look at the manual. Open the supplied manual of the pump manufacturer and it is clearly indicated that a centrifugal pump in foundation design must be perfectly aligned before the pump can be put into use.

In practice however, many pump users still appear to be of the opinion that the pump is already aligned by the pump manufacturer and that on-site alignment is no longer necessary. Why then is this essential?

Photo: Alignment of a pump - credit Oveducon

How does this phenomenon arise? If the shaft exiting the motor and the shaft exiting the pump housing are not perfectly aligned by means of a coupling, the pump will not run smoothly. Compare it to a cyclist who has to try to win a long time trial with a big bend in his wheel. As with the cyclist, the misalignment of the pump also causes increased vibrations and heat production, in this case on the motor and bearings. The lifespan of the mechanical seal is also under pressure due to the many vibrations.

What are the consequences? A pump housing / motor combination that is not or incorrectly aligned will not turn smoothly. This creates extra friction in the bearings, as a result of which the temperature in the bearing can rise to above 90 ℃ with a pump that is pumping water at 18 degrees Celsius.

Photo: Image with thermal imaging camera - credit Oveducon

You don't have to be an expert to understand that a standard bearing with standard grease cannot withstand this for long.

There are also excessive vibrations that can sometimes even be perceived in the floor. If you let something vibrate long enough, everything will break down due to material fatigue. Pump support and mechanical seals are no exception.

In fact, some experts claim that >25% of all damage to centrifugal pumps in this construction is due to misalignment.

For those who want to take into account the energy consumption of the installation: in practice, a Dutch water board has measured that + - 5% less energy is required due to correct alignment.

Damage to the pump is manifested by:

- bearings that fail because the grease runs out.

- motors with a short life due to bearing problems.

- frequent defects to the mechanical seal.

Photo: A loose pumpfoot - credit Oveducon

- pump supports that vibrate loose, putting further pressure on the alignment.

- links that tear or break; there have even been cases of couplings that explode with such a bang, that the pieces flew right through the wall of a sea container. You don't want to be close to that.

- even cracks in the pump foundation.

How can this be prevented? To guarantee an optimal service life, the pump installation must be properly aligned before commissioning. If necessary, the alignment should be checked not only in "cold", but also in "warm" condition.

But then you are not there yet.

The alignment must be checked again every time the pump setup has been tinkered with. It is not enough to put the pump back on the used shims after overhaul and to reassemble everything at the same time. This may sound unlikely, but it is common in practice.

Hope you all enjoyed this article. Please let me know if you have any questions, additions or want to share some of your own experiences!

Next week: number 9.

#maintenance #engineering #engineers #pumps #pump