Pump Curves 1

[npf]

All:

I have some problem on reading pump curves. I have pump curve and pump datasheet for an existing pump, I am trying to determine differential pressure for my maximum nad minimum flows.
Right now the datasheet shows rated case flow, impeller size and impeller size for the max case.
Does that mean for my max case I have to use max impeller size and dtermine my total discharge head using pump curve and what about the min case, what impeller size should I use.

Any help would be appreciated

Regards,

sp77

 

[quark]

We shouldn't have to change impellers for different flowrates(no pun intended). We generally do it by controlling a valve or increasing or decreasing the speed of the prime mover.

For any given impeller size, the pump acts as per its performance curve. Suppose, if you chose the pump at BEP, with an increase in flowrate, the operating point shifts to the right on the curve and thus pump head decreases (infact, it is the other way round, discharge increases when total head decreases).

If you are decreasing the flowrate by creating pressure drop across a valve, head increases (now this point will be to the left of BEP)

If you want to have your operation as good as changing impellers for different flowrates, you have to go for a vairable speed pumping system.

 

[25362]

Centrifugal pump characteristic HQ curves are, in general, of three types: flat, steep and drooping. Each type has advantages and disadvantages. Items such as impeller sizes, types of curves, and variable speed drives, have been discussed in past threads.

A few examples:

thread407-101056
thread407-108359
thread164-100488
thread124-129557
thread124-122503

H: differential head; Q: flow rate.

 

[TD2K]

Pump curves can be simply the curve for the installed impeller OR they can have several curves shown for various sized impellers.

If you are evaluating an existing pump, start with the existing impeller size which should be on the data sheet. Alternatively, you can identify the impeller curve by plotting the rated flow and head point on the pump curve chart and then using the affinity laws to create a pump curve for the installed impeller.

If your existing impeller won't work then I would start considering if a larger impeller up to the maximum will do the new conditions. Two points to consider if you go to a larger impeller: check your power requriements versus what the installed motor can provide and check your NPHSR.

 

[Ashereng]

sp77,

If you are not sure of the installed impeller, I would suggest you open it up and take a look when you can.

The "installed" impeller on your datasheet is what was shipped with the pump from the vendor.

Once you know the size of your impeller, that is the curve you read.

Like someone else said above, if your impeller is not on the pump curve, you can build one using affinity laws.

Goulds Pump has all of this, and more, information on their web site for free.

Disclaimer: I am not associated with Goulds.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Ashereng]

sp77,

Here is the link:

http://www.gouldspumps.com/cpf_0010.html

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[npf]

Thanks all!!!

Regards,

sp77

 

[roker]

hello sp77,

just remember the curves (head versus flow)are for water, so when dealing with
motor power the density of the pumping fluid should be considered.

regards,
roker

 

[Ashereng]

Just an additional note to roker reminder.

Read the pump curve. Not all pump curves are done in water. It depends. I have had some pump curves that was done in my process fluid - I guess someone asked them for it?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[roker]

hello Ashereng,

Was the fluid with high viscosity? the tests of the pumps were also done with your process fluid?

thanks,
roker

 

[Ashereng]

Yes.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?