MIL-HDBK-1003/6
(a)
Minimum Allowable Pump Suction Pressure.
(13)
EQUATION:
Px = Pa + (NPSHa - NPSHs) x S.G.
2.31
where:
Pa
=
Feedwater pressure (absolute) at pump suction, psia
Px
=
Minimum feedwater pressure (absolute) at pump suction,
PSIA, plus the difference between NPSHa and NPSHs.
NPSHa =
NPSH available in feet of liquid of system at shut-off
(Usually static suction head if water in heater is at its
vapor pressure point.)
NPSHs =
NPSH in feet of liquid required of pump at shut-off.
S.G.
=
Specific gravity of feedwater at pumping temperature.
(b) Maximum Allowable Temperature Rise Across the Pump:
EQUATION:
R = Ts - Ti
(14)
where:
R
=
Allowable temperature rise in degrees F.
Generally
limited to 15 degrees F (8.3 degrees C).
Ts
=
Temperature in degrees F corresponding to saturation
temperature of P.
Ti
=
Temperature in degrees F of feedwater at inlet of pump.
Temperature rise and by-pass requirements to prevent damage to the
pump due to cavitation are generally available from the manufacturer.
(c) Minimum Pump Flow
(15)
EQUATION:
Q=
BHP x 5.1
R x S.G. x S
where:
Q
=
By-pass capacity in gpm
BHP =
Horsepower inlet at shut-off.
R
=
Maximum allowable temperature rise degrees F.
S
=
Specific heat of liquid.
148
Previous Page
