Pump Seizing

[aalexsantoss]

Hey all,

I am a mechanical seal engineer and in my current role I have been tasked with learning pump troubleshooting.
I have essentially 2 questions:
1.) What are some main factors contributing to centrifugal pumps seizing up?
2.) Is there a good guide online or book that specializes on centrifugal pump troubleshooting?

Thank you!

 

[Artisi]

The best way to learn about pump problems and the rectification is to get your hands dirty, that means hands on practical experience.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Xalii]

From my experience, the biggest problem for centrifugal pump is the notion of "safe side".
The working point should be as close as possible to the BEP (best efficiency point), but often engineers tends to exaggerate head losses, and take some "safe side" for the head, and the pump is over-design, thus running at the left of their BEP, which means risk of : cavitation, vibrations, overheating, more axial and radial trust, etc...
I think you should knowwell how to design and install a pump, then you can see what is done wrongly. That for you can read the good documents from the pump suppliers like KSB or Grundfoss.

 

[Artisi]

There are many sources to access trouble shooting pumps, probably every manual supplied by any major company will have a brief section - some comprehensive section on trouble shooting - spend some time, do yourself a favour and search it out.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[StoneCold]

Centrifugal pumps rarely seize up. They break down, for many reasons. If you read a lot of articles about pump problems you will see that a lot of the time you don't have a good handle on the suction pressure and on the discharge pressure of the pump. If you can get gauges installed on both sides of the pump it will go a long ways to giving you the information to solve the pump problem.

The only time I ever saw a pump actually seize up it was a vacuum residue tower bottoms pump. The pump was not designed to transfer 900F oil. The metal clearances were not large enough so when the pump got hot it would seize. Once it cooled off it would run again. It was very hard to figure out because the pump was half way around the world from where I was trying to fix it from my desk.

I agree that there is no substitute for going out to the plant and listening to the pumps on a regular basis. Touch them, feel how they vibrate when there is no problem, note how hot they are, note how hot the
motor is. Make sure the motor fan is actually blowing air over the motor. Things like that.

If you want to get better at centrifugal pump troubleshooting you need to read about them, listen to others, and do some hands on work on the pumps, or at least watch them get torn down and see what is happening. Get a good flashlight. Sometimes the light is not so you can see what is going on, but it focuses your attention on a very narrow spot that can be helpful. It also works as a pointer when talking to the operations staff so you are sure you are on the same page.

Regards
StoneCold.

 

[1gibson]

Why does anything lock up? Contact between the rotating and stationary elements, or foreign object in between the rotating at stationary elements. Think of all the ways you could get there. Foreign objects are easy, could be something the pump ate, could be shavings from wear rings rubbing. Contact is also pretty easy, something is reducing the running clearances. Could be thermal, could be misalignment, could be a concentricity problem in the machined parts.

 

[EdStainless]

The other issue is thrust outside of the design range because the flow is outside of the design range.
Too much unbalanced force can also lead to mechanical contact, damage and seizing.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[dbill74]

Something to keep in mind, at least for small close coupled inline centrifugal pumps is proper installation.

Earlier this year had a 3/4 Hp close coupled inline centrifugal pump fail. A new pump was installed under warranty and it failed just a couple months later. With second pump's failure, did a little digging and learned that the pump was installed with the motor housing in the vertical position. Checked the O&M manual and found that this orientation was not a manufacturer approved orientation. Opening the pump to inspect the impellor, found the impellor shattered (no joke), and a retaining ring bent out of shape. Conclusion was that due to the motor housing being in the vertical position, the impellor and rotor assembly fell out of position via gravity causing the impellor to rub against the pump housing until it eventually destroyed itself; not sure if it ever actually siezed or not.

On a side note, whether due to trying to overcome friction of rubbing with the housing or turning a siezed impellor or no impellor to turn, the motor overheated and wiring in the control housing burned out the connections.

 

[cponnu]

If the duty point is close to shutoff ( a thumb rule is is that the same should be more than 15% of best efficiency point), the radial forces on the shaft increase. In case of cantilever type impeller pumps this can lead to excessive deflection which in turn can lead to many issues including impeller wearing rings touching and seizing (in-spite of hardness difference between rotating ring and stationery ring), shaft breakage due to fatigue (in extreme case), sleeve seizing, seal failure etc..

 

[DubMac]

You would get a more meaningful answer if you supplied more detail about what applications the pumps you are responsible for are in (if any one particular industry). API process pumps, large water moving pumps, paper stock pumps, sewage pumps, HVAC pumps each have their own peculiar foibles.

Confucious say: Very broad, ambiguous question get very broad, ambiguous answer.