pump operating in parallel

[vallejo]

I am calculating a H-Q problem. I've calculated the performance curve for a single pump and graphed the solution for varing flow rates. Now, I'm struggling with calculating a pump curve for two pumps operating in parallel. I know to use the pump curve for the single pump and by doubleing the flow rate for each value of TDH should give me the pump curve for the combined pumps. I know it's simple, but I've created a brain lock for myself. Can anyone assist with this simple solution. Thanks in advance.

 

[pardal]

Hi Vallejo:
I think you can read spanish , if so, I have an article that splain it how to deal with it.
Please contact me at
k281969@hotmail.com


Pardal

 

[KernOily]

I agree, this can be tricky. Easiest way is to make a table that has a head column and a capacity column. In the head column, write down the head in multiples of 50' or whatever the pump curve axis division is. Then, reading from the pump curve for that impeller diameter, write down the capacity that corresponds to each head.

When you get that done, continue the capacity column downwards until you get to about twice the pump's single curve capacity. For example, if your pump runs out on the right side at 500 gpm @235' TDH, (sorry for the USCS units, but I went to engine school in Oklahoma... ;-) ), continue your capacity colun down to about 1000 gpm. Then, for every head value , you double the capacity value for two pumps operating in parallel., i.e., two of this pump will deliver 1000 gpm into 250' TDH. Now plot this second set of values on your same manuafacturer's pump curve and draw a line through the points. That is your pump curve for two pumps on-line. Same procedure goes for three, four, or x pumps on line. Note that your pump curve starts to get pretty dang flat.

OK, that's the easy part. The hard part is plotting your system curve on the pump curve so you can determine your actual operating point when both pumps go on-line. You DO have a system curve, right? ;-)

Hope this helps! Thanks!
Pete
pjchandl@prou.com

 

[MortenA]

And the easy way:

Do it in a spread sheet Plotting is also fairly easy here

Best Regards

Morten