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Subtracting the feet of head required for lift (240

we can convert this point to PSIG:

Maximum pump cut-out  = 420 feet 

Less lift 

= 240 feet 

 

 

Maximum pressure 

= 180 feet

To convert feet of head to PSIG, we divide by (2.31) 

(there is (2.31) feet of head for each PSI): 

180  ÷  2.31 = 77.9 or 78 PSIG.
Or pump cut-out pressure (P3) is 78 PSIG.

To Summarize:

We have used actual pump performance as shown 

on the pump curve for the pump selected, to complete 

step one in utilizing maximum capacity of the full 

acceptance 

Well-X-Trol

®

 models, Series 420 and 

450.
In this step we have determined:

  System minimum pressure of 30 PSIG. To 

establish the 

Well-X-Trol

®

 precharge pressure.

 (P

1

) Pump cut-in pressure (P

2

) of 30 PSIG.

 Pump cut-out pressure (P

3

) of 78 PSIG.

Step Two – Determine, ESP volume 

required to control pump cycling. 

Determine average capacity in GPM:

With larger pumps, capacity, or flow of the pump will 

vary depending upon the pressure or feet of head at 

which it is operating.

Even though the pump may be rated as a (85) 

GPM pump (as in our example) the actual capacity 

in GPM will vary as the pump operates throughout 

its pressure range from pump cut-in (30 PSIG) and 

pump cut-out (78 PSIG).
So, we’ll go back to our curve and determine what 

capacity in GPM the pump will deliver at its cut-in 

point, and what capacity in GPM it will deliver at its 

pump cut-out point. Then, we’ll average these two 

capacities by adding them together and dividing by 

two.
Reading the curve, we can find the point that indi-

cates pump cut-in.  We already know that this is:

30 PSIG x 2.31 

= 70 Ft. of Head 

Plus “Lift” 

= 240 Ft. of Head 

 

 

Point on Curve 

= 310 Ft. of Head

0

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TOT

AL HEAD IN FEET

CAPACITY IN GPM

EFFICIENCY 

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Reading down to capacity we can determine that, at  

(310) feet of head, the pump will deliver 

(106) GPM

.

We then read the curve to determine the capacity at 

pump cut-out:

78 PSIG x 2.31 

= 180 Ft. of Head 

Plus “Lift” 

= 240 Ft. of Head 

 

 

Point on Curve 

= 420 Ft. of Head

Capacity at (420) Feet of Head = 90 GPM

Determine ESP Volume:

Being a large pump, we will want to have a mini-

mum run time of at least (2) minutes on the pump:

Average Capacity  Average Capacity

at P2:  106 

98 GPM x 2 = 196 ESP Volume

at P3:  + 90 

 

 

 

196 ÷ 2 = 98

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CAPACITY IN GPM

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