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# Pump rated capacity

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## Pump rated capacity

(OP)
I am going to size a centrifugal pump to transfer liquid from one plant to another plant through 2 km pipeline.
maximum flowrate which could be transfered by pipeline is limited by downstream plant and is around 40 m3/hr.
since maximum flowrate is fixed , i am not sure that is it still required to consider some margin(e.g. 10%-15%) over this maximum flowrate(40m3/hr) for calculating rated flowrate(44-46m3/hr) of pump?

### RE: Pump rated capacity

This is probably something that only you can answer.

Here are perhaps a couple of points to consider.

1) How critical is it to get exactly the right flow. Is there major consequences if flow is a little faster or slower than the 40m3/hr.
2) How accurate is the data that you are using to size the pump eg: static head , pipe lengths , roughness etc.
3) Is there any issues on budget , complexity , operational that would impact on the selection.

If flow is critical and it must be close to 40m3/hr and perhaps some of the data is not well tested, you could select a pump using what you have that might do about 45- 50m3/hr and fit a VFD so that you can adjust the speed to give you exactly the flow you require. Likewise you would have a bit of reserve capacity if there is a bit more head than expected.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

### RE: Pump rated capacity

(OP)
Dear Ashtree;
thanks for you reply,
maybe i need to answer to matters you raise one by one:
1)flowrate of 40m3/hr is design capacity of downstream unit.
2)all activities are actually expansion in existing facilities,it means 3dmodel of boat plant is available,so new pipe length and static head could be calculated with good accuracy.
3)there is not any especial issue on budget,about operation it is important to mention that downstream unit is common unit for two plants which should be utilized sometime by one plant and other time by another plant.what I asked is only technical/operational negotiation.
We are going to install a Flow control valve downstream of pump.
Regards

### RE: Pump rated capacity

Well if you are going to put a flow control valve in then you could argue that you put a slightly bigger pump in to give something for the valve to control. You will waste some energy but it does also give you a small margin for things like wear in the pump , accumulations in the pipeline etc.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

### RE: Pump rated capacity

Size for what you know.

If 40 m3/hr is max flow then size for that, especialy if the piping is well known and required head is known within a few metres.

Take care that when you look at the fferings from vendors, you choose a pump where your rated / max flow/head is just on or judt ot the left of BEP ( Best efficiency).

Work out actual electric power being used and you may well find, if this pump is used a lot, that what is the cheapest pump would cost you many more  in electricity if it is not as efficient as the next one.

Oversizing of pumps is rife and just leads to lots of energy wasted all over the world.

Size for what you know.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Pump rated capacity

(OP)
thank you very much my friends

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