7 replies to this topic

[icingrock]

I am sizing a pump for a new process conditions and try to use the same model with some of the existing pump to have synergy in terms of spare pumps.

The pump suction pipe is 4 inches with discharge pipe 3 inches. The pump is sized with suction flange of 3 inches and discharge flange of 1 1/2 inches.

The normal process flowrate is about 100 to 120 gpm with hydrocarbon liquid (used as solvent).

The pump itself fits in to the process conditions from my judgement. My Question is if the pump discharge (of 1 1/2 inches) is adequate to fulfill 120 gpm flowrate. Of course, there would be no problem with discharge pipe (of 3 inches).

And what's the rule of thumb for sizing pump suction/discharge flange in comparison with pump suction/discharge piping ?

Thank you.

[breizh]

http://www.practicalpumping.com/

For the last question consider the resource attached (pump piping video).

Hope this helps
Breizh

[icingrock]

Breizh,
I read through the website it said the pump nozzle should be one size smaller than the pipe size both for suction and discharge side.

But it did not say if more than that is ok.

Please advise.

[breizh]

It's mentionned that the pipe must be one size bigger than the suction and discharge nozzles with appropriate concentric and excentric connections .


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

Breizh

Edited by breizh, 26 February 2012 - 10:36 PM.

[S.AHMAD]

And what's the rule of thumb for sizing pump suction/discharge flange in comparison with pump suction/discharge piping ?

1. There is no specific relationship between pump suction/discharge nozzles to that of piping size.
2. For new design, pi[e size is based on pipe economic size and the pump capacity is selected that meet the system characteristics.
3. For an existing pump, the piping size is selected such that the system characteristic curve falls within the pump characteristic curve.
4. The suction piping is sized based on the NPSH requirement of the pump to prevent cavitation.
5. The above comments are for centrifugal pump.

[icingrock]

S..AHMAD:

so it's reasonable to size the pump nozzle to 1 1/2 inch in my condition.

[Art Montemayor]

Icing:

Please allow me to comment on what I believe Breizh and S. Ahmad are advising you:

The service that the pump can handle is stated in its Performance Curve. In other words, your centrifugal pump will handle the rated capacity at the rated head as expressed in the Performance Curve. If your pump can meet your design conditions, then it is applicable – regardless of what the manufacturer has selected as the suction and discharge nozzle sizes. Centrifugal pump casings and bodies are cast well in advance of being assembled and sold as a working pump. No successful pump manufacturer is going to begin to cast a centrifugal pump casing in accordance with YOUR nozzle sizing specifications. And if they do, you probably won’t be able to afford the selling price. What they will do is to select the appropriate casing size (and nozzle sizes) that will do the rated job.

It is then your job to take the delivered pump and apply it to your service by hooking up the associated piping, electrical, and instrument connections. The piping usually calls for an eccentric reducer on the suction flange (with the “belly” portion down) and a concentric expander on the discharge side. The reasons for this conventional necessity is because one always needs to ensure that as high an NPSHa is available in the suction side and as low a pressure drop is attained in the discharge side.

What is confusing to everyone is when you state that “it's reasonable to size the pump nozzle to 1 1/2 inch in my condition”. You certainly are not in any position to size the pump’s nozzle or dictate it to the manufacturer – especially on an existing pump. You are not the “pump expert” of record. The pump manufacturer is. Therefore, simply take the manufacturer’s pump and apply it with the installed piping as indicated above – but only if the pump’s authentic Performance Curve shows that it can meet your process conditions.

If the Performance Curve shows the pump is applicable, there is no issue between the pump's nozzle size and the required process piping size it is connected to.

[S.AHMAD]

1. Art has given you a detailed explanation. Let me directly reply to you question.
2. Pump vendor/manufacturer has several pump models of various capacity and performance curve (Head vs Flow)
3. Our function as a process designer, is to select the pump of the right capacity and the right impeller size such that the system operates as near as possible to the BEP. REGARDLESS OF PUMP NOZZLE SIZE.
4. Most of the time, we ask several vendors to propose the right pump. We provide the system hydraulic requirement and select the proposal that satisfy our needs.