Different Pumps

Different Pumps

Operating two different size pumps in parallel the assumption is made that the flow will increase dramatically. This however is not the case. In order to calculate the additional flow realized by running two different size pumps in parallel the following calculations must be made.

System Head Curve

First let's look at the pump curve and system head curve with the 3" pump running.

TDH	FLOW
90'	0 GPM
87.5'	50 GPM
85'	100 GPM
80'	160 GPM
OPERATING POINT (A)
70'	300 GPM

Second let's look at the pump curve and system head curve with the 4" pump running.

TDH	FLOW
90'	360 GPM
87.5'	410 GPM
85'	460 GPM
80'	470 GPM
OPERATING POINT (B)
87.5'	410 GPM

Third let's look at the pump curve and system head curve with the both the 3" & 4" pump running.

TDH	FLOW
90'	360 GPM
87.5'	460 GPM
85'	560 GPM
80'	580 GPM
OPERATING POINT (C)
87.5'	460 GPM

With the 4" pump running and then adding the 3" pump produces an extra 50 GPM. Point D is the flow produced by the 3" pump when both pumps are running. Point E is the flow produced by the 4" pump when both pumps are running.