Pump Failure

[Emrelug84]

Hi Guys,
We have a boiler feed water pump operating. Recently, i have learned that it stopped working. Pump has been tripped. Shaft is not able to be turned by hand. I have checked cavitation theoretically, eveything is good.
Moreover, when pump is not in operation water temperature drops to 50oC at suction side and operation water temperature is 150oC. When pump is in operation 50oC and 150oC water are mixing at suction side. Do you think this affect pump performance in a negative way? Do you have any suggestion to solve the problem?

Thanks.
Emre

 

[chicopee]

My first thought would be pump bearings seizing on the shaft.

 

[Artisi]

Firstly why post here, you would be better in the pump engineering forum.

However, dismantle the pump and have a look is the best solution - theorising won't fix it.

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.)

 

[Emrelug84]

Thank you chicopee. It makes sense for me. I focus on that issue.

Artisi, as we are engineers, i certainhly post here. I believe that somebody will help, you may not.

 

[Artisi]

Can just repeat my advice, you are better off on the pump engineering forum but that's up to you and depends on how many pump guys you want to view your post.
My comment stands, don't theorise -, run some basic checks.

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.)

 

[Strong]

If the pump stopped while running, then you can expect serious internal damage. If the pump was off and shaft would not rotate, then there could be a thermal gradient on pump case that is causing binding. I worked on a 9000-hp 2-stage centrifugal pump (1 of 3) at a nuclear plant that had this issue. It had been disassembled by others and no internal issues were found. They were also blaming shaft misalignment. My associate measured the temperature difference across the case and we found that the warm-up piping was incorrect. A sim[le fix to allow the shaft to rotate freely. Big problem and little fix!

Walt

 

[Emrelug84]

Thanks guys,

Pump manufacturer had already come and dismantled the pump. The only statement from them is the problem is because of suction condition and it is out of warranty. However, they did not explain the reason of the problem in detail. I try to analyze operating conditions. Pump's flow rate is approximately 500m3/h and it is operated at between 20 and 76m3/h flow rates for 50min. These flow rates are far below the minimum operating flow rate of the pump. I think it means dry-running issue as Chicopee gave a clue about that.

Regards,

Emre