9 replies to this topic

[trungphu]

Hi everyone,

 

Could anyone here explain me why the outlet pipes of pumps are always designed to be smaller than the inlet?

 

Thanks in advance,

 

Trung Phu

[breizh]

http://www.mcnallyin...2-html/2-7.html

The link attached may support your work .
I would be more cautious about the size of the inlet pipe ( NPSH). For the discharge pipe it's an optimization between Head loss and cost.

Breizh

[fallah]

 

Could anyone here explain me why the outlet pipes of pumps are always designed to be smaller than the inlet?

 

 

Trung Phu,

 

Mostly because the fluid velocity in suction line should normally be lower than fluid velocity in discharge line to increase NPSHA and having smooth flow at pump inlet...

[Zauberberg]

In addition to the answers above, see:

 

https://www.grundfos...siderations.pdf

http://www.pumpfunda...pump_system.pdf

[trungphu]

Thank all for your valuable comments.

 

Mr. Falllah,

 

I also wonder whether the reducer at the inlet of pump is designed to increase NPSH or just to fit the pump inlet.

 

Regards,

[samayaraj]

Pump suction velocity will be near or less than 1 m/sec and discharge velocity will be nearly double the suction velocity in many cases. Lesser the velocity at suction lesser the pressure drop and more head will be available at the pump suction to avoid cavitation.

Generally pump suction/ discharge size will be less than one or two sizes below the the pipe size. This is because to limit the pressure drop in piping system within the limit by providing one size bigger than the actual requirement. On the pump vendor side, he has to optimize the pump size, so the velocity at the pump nozzle will be higher than the pipe resulting in one or two size smaller.

[samayaraj]

Thank all for your valuable comments.

Mr. Falllah,

I also wonder whether the reducer at the inlet of pump is designed to increase NPSH or just to fit the pump inlet.

Regards,

Reducer is provided just to match the pump suction size to the pipe size. Always there will be eccentric reducer with flat side up provided in suction of pump to avoid any gas/ vapor entrapment.

[breizh]

Hi ,
Good to read

Breizh

[fallah]

Thank all for your valuable comments.

 

Mr. Falllah,

 

I also wonder whether the reducer at the inlet of pump is designed to increase NPSH or just to fit the pump inlet.

 

Regards,

 

Trung Phu,

 

The reducer, if needed (there might be the cases in which the suction line size is equal to pump inlet nozzle size), at the pump inlet has to be considered just to fit the pump inlet nozzle size with suction line size. Obviously, it would have a negative effect on NPSHA of the pump...
 

[trungphu]

Thank all for your valuable comments