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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
100
200
300
400
500
600
700
20 40 60 80 100 120 140
20
40
60
80
TOTAL HEAD IN FEET
CAPACITY IN GPM
EFFICIENCY %
EFF.
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
0
100
200
300
400
500
600
700
20 40 60 80 100 120 140
20
40
60
80
TOTAL HEAD IN FEET
CAPACITY IN GPM
EFFICIENCY %
EFF.
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