Reading Pump Curve (Total Head Axis)

[code1]

Dear all,

The total head (m/ feet) for a given pump curve, is it always in pressure atmosphere or pressure gauge?

Eg. reference the pump curve Total Head H in Page 8. No atmosphere or gauge is stated. So which is it, A or G?

http://www.gouldspumps.com/download_files/ic/bicfamily.pdf

Is there an industry norm that I am not aware of?

 

[JoeySoap]

It's increase in head across the pump.

 

[katmar]

The pump head is a differential pressure between the pump suction and discharge and is therefore neither absolute or gauge.

This is similar to the pressure drop down a pipeline - which is also a differential and therefore is not specified as absolute or gauge.

Of course a point pressure at the pump discharge or anywhere along a pipeline can be specified either as absolute or gauge, but not when we are looking at differentials.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[code1]

This is also what I thought.
But when I read the corresponding gpm vs. H, the reported value in the technical datasheet could not be reconciled with the curve.
Datasheet:
Vendor pump data was reported with suction = 1.2 barA, differential head = 103m =~ 10bar.
Discharge would then be 11.2 barA.

Curve:
At duty gpm, Total Pressure head H read off was 11 bar.

(Il)logical conclusion, the curve of total head H was reporting discharge pressure? Else, should have obtained 12.2 bar A discharge (=11 bar differential head + 1.2barA = 12.2barA)

 

[quark]

How did you find the actual differential head to be 103m? Check suction pressure from suction line gauge and discharge pressure from discharge line and the difference gives you differential pressure. Secondly, pump curves are approximation and will give you results close to the actual conditions but not exact matches.

 

[code1]

I was reading a pump spec + datasheet submission by a vendor. Want to relate the spec data to the curve.

It is one of those instances where a difference of 1 bar makes a difference to the calculation (theoretically).
Else, I may just have shrugged it off..

 

[GPRnD]

Are you sure the vendor data is quoted in bara and not barg ?

Also presumably the density of your fluid is close enough to water to allow your conversion from 103 to 10 bar ?

 

[Artisi]

Remember, the head shown on a pump curve is head that can be generated in ft / metres, not a pressure, it can only becomes a pressure when you consider the S.G. of the pumped product.

For example, if the pump can generate X metres it is X metres at SG 1 or SG 3 or SG 0.7.

 

[JoeySoap]

That's right, first of all you need to do a correction for discharge pressure at the SG of the fluid. Then you can relate pressure to head, but not before.

 

[code1]

Dear all,

Thanks for your advices.
FYI, it is water (condensate at 85 deg. C) that I am looking at. Sorry it was not stated earlier.

I called the Pump Manufacturer directly to discuss the pump curves, and was offered the possible explainations (which I will re-confirm with the Vendor):
1. to check the actual impeller installed
2. the Vendor may have used an actual curve from a previous project to submit to me
3. Motor speed in the pump curve maybe different from the data in the datasheet

However at a later date I will review the pump performance test data to verify.

Thank you all for your inputs.

 

[Artisi]

code1

Points 1 & 2 seem reasonable comment but point 3 doesn't make a lot of sense unless of course you are talking about the difference between say 2 pole and 4 pole speeds, if you are talking about a few percent difference in running speed resulting from slipage then it doesn't account for much in the way of head.