Centrifugal Pump Suction Conditions 3

[Enginator]

We are installing a centrifugal pump downstream of a close-packed hydrocyclone. The hydrocyclone vendor was concerned that the pump would draw on the cyclone and reduce cyclone performance.

It is my understanding that centrifugal pumps don't "suck." Are there any conditions that would cause the pump to affect upstream conditions?

John

 

[checman]

Enginator: It all boils down to the pumps NPSHR (Net positive suction head required) this is based on the amount of energy required to over come the entry losses of the pump. And the systems NPSHA (Net positive suction head available) Both NPSHR and NPSHA are always given in absolute terms unless otherwise stated. Nether calculation takes into account the pumps ability to suck but NPSHA does take into account atmospheric pressure and gravity (if the suction is flooded) to push the liquid to the pump. That is why it is said that pumps don’t suck they just create a void for atmospheric pressure and in some cases gravity to push the liquid to the pump.

DJMiner: The suction bell is to overcome a suction pipe inlet problem, most likely minimum submergence. If you can handle the suction losses of a 12” x 24” reducer you can probably just use one of those.

ynot3737: Lets say your pump is 2.31’ below the surface level of your pool. Lets also say your pump can produce 25 psi. Finally lets say your filter is really dirty and you have 20 psi differential pressure at your pumps recommended minimum flow. Not taking into account any friction losses if the filter is on the discharge side you would get your minimum flow. If the filter was on the suction side you would not get minimum flow. If you were at sea level you would have approximately 14.7 psi + 1 psi suction head or 15.7 psi available (not taking friction losses into account). That will not over come the 20 psi differential pressure from the filter at the pumps minimum flow.

Regards, checman