Understanding Centrifugal Pumps Efficiency vs. Flow Rate Curves 1

[Pavan Kumar]

Hi All,

I want to tabulate the pump efficiency vs. flow rate for a pump that I am doing power requirement calculation. As you can see in the attached pump curve, the efficiency curves are the looping curve extending over a range of flow rates. I want to tabulate the pump efficiency vs. flow rate and use this table to accurately calculate the pump shaft power and the full load amps for the motor. I looking to get a parabolic curve with the maximum pump efficiency at a certain flow rate. How do I do that?. Can I ask the pump manufacturer?. Does the pump efficiency vary with impeller size and RPM?.

Also does the pump efficiency change with the system resistance. in my case the duty point is at 3046 gpm at 75 ft head. From the pump curve the pump efficiency is 83%. Now if I lower the system resistance by increasing the discharge line size from 10" to 12" the head developed reduces the duty point moves to the right. Depending on where the duty point the pump efficiency could either increase or decrease. I will calculate the duty point for this scenario shortly.

Thanks and Regards,
Pavan Kumar

 

[Pavan Kumar]

Hi All,

Thanks for your suggestions I will now finish my calculations and prepare my comparizon for various options today.

Hi Littleinch,

I will evaluate the option of the control valve too.

Thanks and Regards,
Pavan Kumar

 

[pierreick]

Hi,
Consider the paper attached, you will find good pointers to support your work. Similar vein.
Pierre

 

[Pavan Kumar]

Thank You Pierre.

Pavan

 

[Pavan Kumar]

Hi All,

Here are the results for the pump options with the various line size options. I am getting the cost of piping ( send piping BOMs to vendors for quotations) for each option further to ROI calculation I will be choosing the line size and hence the operating point.

I have another question. So far a pump that is spare( North Tepid Pump) to this pump under question( South Tepid Pump the vendor gave me the efficiency vs. flow rate curve that is attached. This is the typical inverse parabolic curve I expected as opposed to the iso-efficiency curves given for the South Tepid Pump. My question is that why don't the vendors always give the inverse parabolic curves and instead give the iso-efficiency curves which are harder to digitalize and use in automated spreadsheet calculations. What are the differences between the two. I was told earlier in this thread the efficiency varies the pump impeller diameter, head. Here ( for the inverse parabolic curve) the efficiency varies with only flow rate. Need better understanding.

North Tepid Pump Curve

South Tepid Pump Curve

Thanks and Regards,
Pavan Kumar

 

[FMJalink]

Hi Pavan Kumar,

The North Tepid pump curve shows the efficiency curve for a 12.25 inch impeller only, where as the graph for South Tepid Pump shows iso efficiency lines in the head - flow field for all impeller diameters.

If you would draw the 12.25 inch impeller head - flow curve in the South Tepid Pump curve, you could read efficiency values per flow rate there from the drawn curve.

The Pump Vendor would gladly provide you desired pump curve, though it will be indicative, as only the test curve gives final data.

Most larger pump manufacturers have selection software allowing Buyers/Engineers to make such curves. Normally representatives or Vendors have to grant you access. Cannot check the types of curves possible with the Goulds software, as I am on my holiday location without access my normal means.

Hope this helps.

 

[Pavan Kumar]

Hi FMJalink,

If I understood you correctly, the pump vendor can provide me the efficiency vs. flow rate curve for each impeller from their software if I request correct?. I will check if I can access / get access to their pump curve software to print the curves myself ( even if indicative).

Thanks and Regards,
Pavan Kumar

 

[FMJalink]

Hi Pavan Kumar,
Correct,the Vendor can provide you the indicative efficiency curve for each impeller diameter.
With the selection software of most larger pump manufacturers one can select also the diameter and get the indicative pump curve. I do not remember for sure, whether this also shows the efficiency curve with the Goulds selection software.
Just ask your Vendor or the local pump representative.
Regards,
FMJalink