Pump Station Suction Pipe

[Engmunir74]

Hello everyone,
I am reviewing a design of water pump station which is fed by an open tank. from the hydraulic point of view, will there be any problem if the impeller level was higher than the tank intake level, although the NPSHr is satisfied and the minimum water level in tank is still higher than the impeller level by 1.5m?, in other words, the suction pipe is going upwards.
Thanks in advance

 

[Artisi]

Can't see any problem, but is there something missing causing you to be concerned and raise the question?

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.)

 

[Engmunir74]

Thanks for your fast response
Theoretically, there is no concern. But my concern has been because I have never seen such case before.

 

[MJCronin]

I agree with the comments above, there should not be any problems because of the elevated suction nozzle.

With only 1.5 meters of cover, it is possible that, at minimum pumping level, you could experience suction vortices.

These are somewhat common with Cooling Tower Water pumps

http://www.baltimoreaircoil.com/english/resource-library/file/552

https://www.youtube.com/watch?v=2MTIoagkpyc

You may have to consider a baffle in the final design

Was there a mistake in the concrete drawings or perhaps a mistake in the amount of grouting for the pump baseplates ?

MJCronin
Sr. Process Engineer

 

[LittleInch]

Agree its not a problem, but sounds to me like a waste of money if the tank minimum level is at least 1.5m plus whatever level the pump is above the base of the tank.

I'm a little confused by what you mean by "higher than the tank intake level" Do you mean nozzle?

A simple sketch always helps in these circumstances.

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

 

[Engmunir74]

Thank you all
Following sketch shows what I mean.
Nozzle level = 104.51m
Impeller level = 106.00m
Minimum operating water level in tank = 107.52m
What I mean by 1.5m, is the deference between impeller level and minimum operating water level (107.52-106=1.52m)
Nozzle submergence is checked in accordance with ANSI/HI 9.8-1998 and found enough (no vortex problems), =107.52-104.51=3.00m

 

[MJCronin]

OK .... much better picture.

As wise men on these for a have said in the past: MORE INFORMATION = BETTER ANSWERS

MJCronin
Sr. Process Engineer

 

[bimr]

Without the complete scheme including heights and velocities, it is hard to say. It may work. Pump suction lines should be as short as is practically feasible. Round suction source vessels can be problematic with regard to vortex formation. A pipe entering the tank from a higher level allow the liquid to free-fall and impact on the suction reservoir’s liquid surface can aerate the vessel’s contents causing pump problems.

http://www.pdhonline.org/courses/m134/m134content.pdf

 

[LittleInch]

Thanks for the sketch, made it much clearer.

No problem hydraulically, just remember a sump type system will collect solid matter faster and you need to have access to it.



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