Goulds Pumps 3408 - IOM - Manual (Page 75)

USEFUL FORMULAS
1) Head (ft.) =
Pressure (psig) x 2.31
S. G.
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:
Where n
m
= motor efficiency, p.f. = Motor power factor, Avg. Amps =
leg 1+ leg 2 + leg 3
3
4) Pump Efficiency (n
p
): n
p
=
GPM x TDH
3960 x BHP
5) Affinity Laws for correcting GPM, TDH, and BHP for speed (RPM):
GPM
GPM
1
2
=
RPM
RPM
1
2
or GPM
1
= GPM
2
x
RPM
RPM
1
2
TDH
TDH
1
2
=
(
RPM
RPM
1
2
)
or TDH
1
= TDH
2
x
(
RPM
RPM
1
2
)
BHP
BHP
1
2
=
(
RPM
RPM
1
2
)
or BHP
1
= BHP
2
x
(
RPM
RPM
1
2
)
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.
68
3408 IOM 03/99
Single Phase Motor
BHP =
Amps x Volts x n x p.f.
746
m
Three Phase Motor
BHP =
Avg. Amps x Volts x 1.732 x n x p.f.
746
m
3
2 2
3
APPENDIX “C” FIELD TEST REPORT