Pump killers: How to fight the 13 most common centrifugal pump failures? Number 6.

In the series “Pump killers” we investigate the 13 most common causes of centrifugal-pump failure and take a look at the measures that can be taken 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.

If we look at the marks left by this week's "killer", we see plastic pipes swelling, borehole discharge lines cracking, borehole pumps burning, rotors getting so hot that the vane melts. In short: heat. This week we therefore look at the phenomenon of "warming up", or "running the pump in its own liquid". This week, too, we encounter the fact that the consequences of certain choices are often wrongly underestimated:

Photo: "A pump that exploded due to overheating."- electricneutron.com

So let's take a look at the theory and how it differs from practice. A centrifugal pump transfers the heat generated in the pump housing by the speed energy to the medium being pumped. When the pump is on and no medium is being pumped, the medium is heated up in the pump housing and the part of the pipe up to the valve that is closed. In theory, a protection should be included to prevent this from running up or running in its own liquid, but as has been shown before: in practice, this is sometimes cut back.

How does this phenomenon arise? Spinning / warming up in your own liquid can occur in various ways. For example, there may be no reduction in the medium while the pump is running, or there may be too little medium that needs to be pumped, so that the temperature can continue to rise.

In addition, we increasingly see that pumps are controlled remotely. In itself nothing against that of course, but this must be done if there is a decrease in the medium. If this is not the case and there is no protection on the pump that can prevent this, you will soon have 'football in your pipework':

Photo: "Swollen pipe due to overheating." - Photo Oveducon

A final cause has to do with where the pump is selected in the pump curve, something we talked about a bit two weeks ago. We already saw then that it is of great importance for the service life and reliability of the functioning of a pump that it is selected for the correct working area in the pump curve.

Photo: "Pump graph with dotted line"

If the pump runs almost to the remote left in the curve, the medium will heat up too much. It is therefore not surprising that in some pump curves the left part of this curve is indicated with a dotted line. With this, the manufacturer is already trying to indicate: the pump should not be selected here!

What are the consequences? If a pump is running without or with too little liquid draw-off, the following things can happen:

Photo: "Swollen plastic pipe." - Photo Oveducon

- Plastic pipes that swell;

- Glue joints that will leak;

- Increased noise production;

- Pump seals that will leak;

- Seal breaks down;

- Greatly shortened service life of the pump;

- Damage to the rotor and windings;

- Pump can explode.

The latter may seem a bit extreme, and it is, but this certainly does happen. If you don't believe us, take a look at: ‘Center for Chemical Process Safety’.

And do not forget the following, namely that too little liquid consumption can cause the medium to heat up to a temperature that is not desirable for the medium properties and / or the process, with, again, all the associated consequences.

How can this be controlled? There are several ways to protect a pump against overheating. For example, a flow protection / switch can be placed in the pipe, a temperature sensor can be mounted in the medium or a pressure protection can be included in the pipe.

Photo: "Medium temperature sensors, both fixed and freely adjustable" – Photo Oveducon

In addition to these protections, care must of course already be taken when selecting the pump that the pump is not selected too much to the left of the curve. For this reason, attention must be paid to the operating points of the installation that must be known with regard to the calculation of the pump. And: do not forget to calculate the media properties in the operating point. Especially in the latter, as often appears during our courses, a mistake is easily made.

We are curious about your experiences with this pump killer, because the videos that we come across on the internet when we search for 'Bleve' are scary to say the least!

We will take a little holiday-break and be back with issue 5 in the new year! Happy holidays!