why design this configuration ?

[sunloco]

I saw a structure drawing of single stage centrifugal pump. From the suction flange to intake of impeller there is a cone-shaped pipe structure.It means the intake is more and more small diameter.who know why use this structure ? how did it work? Is there any advantage for NPSH or others ?

 

[insideman]

The tapered inlet is important to make the flow more uniform across the diameter. Good for efficiency.

 

[sunloco]

Is there any use for NPSH? or nothing with NPSH?

 

[Bjegovic]

head loss in conical flow confusers (gradual decrease in diameter) is much smaller than in difusers. So it has no big adverse effect on NPHS, and benefits come from the other side.

 

[Artisi]

What size is the pump inlet flange and how long is the tapered cone shape?

It is possible that the impeller eye is "X" diameter -- but the pump inlet flange is sized to suit a particular pipe size, therefore the best configuration is to have a conical inlet to the impeller eye.

For example - the impeller eye might be 160mm diameter, the next pipe diameter is 200mm nominal bore, therefore you would expect a 200mm inlet flange.
I doubt if it has anything to do with NPSH design.

Naresuan University
Phitsanulok
Thailand

 

[JJPellin]

I am not certain that I understand exactly what you are describing. But two possibilities come to mind. The conical section could be there to increase the velocity coming into the impeller eye in order to avoid suction recirculation cavitation. The pump would have a small impeller eye and thus a fairly high Net Positive Suction Head required. The pump would be designed for low suction specific speed to avoid suction recirculation at low flow. The conical transition would accomplish this, but would increase the NPSH required and could lead to a problem with low suction head cavitation if you don't have an adequate suction head margin. The other option that occurs to me comes from a self priming pump design that is common in shallow well pumps. In those pumps, the conical section is actually an inducer using discharge flow to induce suction into the impeller. This helps the pump run with very low suction head and makes it somewhat self-priming. But that would require internal ports to direct discharge flow through that cone. If there are no discharge ports, then it is there to reduce suction specific speed and avoid suction recirculation.

 

[Artisi]

JJPellin (Mechanical)
Not sure if your post was in response to my earlier posting, if it is, I am happy to rephrase and clarify my thoughts.


Naresuan University
Phitsanulok
Thailand