Grundfos vertical CR8 pump screaching noise on shutdown

[Miguel Costa]

Good Afternoon!

I have just came from an installation where there is a Grundfos water pump (CR8)that makes a loud screeching sound when it turns off. Amp draw is OK 5,8 Amps on all 3 phases, pressure increase is normal compared to 2 other exact pumps that are in parallel, voltage across the 3 phases is ok (388 VAC). Seems to work fine, but it always makes that loud screeching sound when it shuts off... Can any one give any insight on this matter? Thanks in advance!

P.S. - I have a video that shows the pump working and turning off with the screeching sound if anyone is interested.

 

[Artisi]

Can you isolate the pump and remove it from the system, it maybe to only way to establish what is happening, otherwise it's all guess work.

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]

A rather short duration impulse event that sounds like a check valve closing.

Walt

 

[Miguel Costa]

Hi artisi, yes i can isolate it, leaving the other 2 doing the work. Next week I'll take a look at it and pull it apart to have a peek inside. Will also look at the fan alignment and check valve imediatly at the discharge end (thanks Walt). I still need permission from the owner to pull it apart, but by Thursday I want to have it done. I'll keep you posted! Thank you everybody!

 

[TugboatEng]

This is one of those cases where you just run it until the problem makes itself obvious (failure).

 

[LittleInch]

Hang on here.

Your schematic shows a pressure tank but no nrvs on each pump. What is stopping reverse flow through each pump?? Can't see any in the photo.

When this pump stops is it always the last pump to stop? What is the operating sequence here?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Miguel Costa]

Hi LittleInch,
You are right, i forgot to draw them, but they are there. In the photo: at the discharge of the pumps right before the shut-off valve of each pump. Sorry about that...
As for the operating sequence, It cycles between each pump, trying to maintain the same amount of hours of use on each pump. Sometimes it comes in first and shuts off first, sometimes only one or two are working, it depends on the pressure drop.
Don't know if it might help but I failed to mention that this equipment is being used in an apartment building 8 stories high, it provides tap water to the top half of the building.