Xylem 8100 Series Centrifugal Pumps AC2515 REV.C - Manual (Page 62)

APPENDIX “C” FIELD TEST REPORT
USEFUL FORMULAS
1) Head (ft.) =
S.G.
2.31 x (psig.) Pressure
S.G. = specific gravity ; S.G. of water = 1.0 at 70°F
2) TDH (ft.) = Total Dynamic Head (ft.) = (Disch. pressure gauge reading - Suct. pressure gauge reading) +
(Discharge velocity head - Suction velocity head) +
(Elevation correction to disch. gauge - Elevation correction to suct. gauge)
3) PUMP INPUT HP (BHP) - calculated:
Single Phase Motor Three Phase Motor
BHP =
746
p.f. x n x x Volts Amps m
BHP =
746
p.f. x n x 1.732 x x Volts Amps Avg. m
where n
m
= motor efficiency, p.f. = motor power factor, Avg. Amps =
3
3 leg 2 leg 1 leg  
4) Pump Efficiency (n
p
):
n
p
=
BHP x 3960
TDH x GPM
5) Affinity Laws for correcting GPM, TDH, and BHP for speed (RPM):
2
1
GPM
GPM
=
2
1
RPM
RPM
or GPM
1
= GPM 2 x
2
1
RPM
RPM
2
1
TDH
TDH
=
(
2
1
RPM
RPM
)
2
or TDH
1
= TDH 2 x
(
2
1
RPM
RPM
)
2
2
1
BHP
BHP
=
(
2
1
RPM
RPM
)
3
or BHP
1
= BHP
P
2 x
(
2
1
RPM
RPM
)
3
6) NPSHA DETERMINATION:
NPSHA = Net Positive Suction Head Available
NPSHA = (Atmospheric pressure - Vapor pressure of liquid + Total suction head)
Total Suction Head = (Suction pressure gauge reading + Suction velocity head + Elevation correction to
suction gauge)
NOTE: NPSHA must always be greater than NPSHR (NPSHA > NPSHR) for the pump to operate without
concern of cavitation.
NPSHR refers to Net Positive Suction Head Required by pump. This is a published value obtained from
the Pump Manufacturer’s curve.
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