Piping Design Centrifugal Pump 1

[Boghi1990]

Hi,

Why the suction and discharge lines have to be one or two sizes larger than the pump connection nozzles? What could happen if the suction or discharge lines are larger than the pump suction or pump discharge nozzles? I would appreciate if anyone can help me with an answer to this topic.

Regards,

One Point

 

[bimr]

For water applications, desirable velocities in pump suction piping are typically 4-6 ft/sec. An eccentric decreaser with the flat side on the top is typically located ahead of the pump suction nozzle to avoid trapping air. Too much headloss on the suction side may cause cavitation damage to the pump. Too much air may damage the pump.

Desirable velocities in pump discharge are typically 6-8 ft/sec.

Don't believe there are any concerns if the piping velocities are lower than typical. Higher velocities will cause more problems than lower velocities.

 

[stanier]

Suggest you get hold of ANSI/HI 9.8 or Sanks's Pumping Station Design. there are also resources at the US Corps of Army Engineers Website.

Another link worth investigation is

http://www.mcnallyinstitute.com.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[Pumpsonly]

The impeller inlet eye dia. is calcualted based on the BEP flow rate velocity of the pump or the impeller.Too high a velocity will lead to high NPSHR. Too low will lead to high suction specific speed and lead to suction recirculation cavitation when operated at low capacity.

Larger suction pipe size is not mandatory if there is sufficient NPSHA.
Bigger suction pipe is necessary if the friction losses is too high and resulted in insufficient NPSHA at the pump inlet.

Similarly, discharge piping dia is depending on the flow rate hence velocity. High fluid velocity has high friction losses which mean more power is required to pump the same amount of liquid than with bigger pipe size.

Other factors to be considered are.

1) Total discharge pipe length.
2) Capital cost verses running cost.

 

[Chance17]

Mr. Bimr -- see attached file.
The flat part of eccentric reducer is not always on top.

 

[bimr]

Thanks for adding to the discussion, but note the word "typically".

You could have added that if you were pumping fluids containing solids, you would also want the flat part on the bottom. However, this discussion is heading off topic.