Milton Roy mRoy B User Manual

23Installation, Operations & Maintenance Manual
SECTION 2 - INSTALLATION
2.11 OPERATION WITH SUCTION LIFT
It is desirable that the mRoy pump operate
with a ooded suction; however, operation with
net positive suction head (NPSH) less than
atmospheric pressure is possible.
NPSH is the head available, above the vapor
pressure of the liquid being pumped, to feed the
liquid into the pump suction port. NPSH minimum
is the head below which the pump cavitates.
Both values are calculated at the suction port of the
pump. In controlled volume pump applications, two
conditions must be considered in the selection of a
pump to meet the NPSH minimum requirements:
1. At the start of the suction stroke, the liquid in the
suction line has no velocity and NPSH minimum
depends on the force necessary to accelerate
the liquid in the suction pipeline.
2. At the peak of the suction stroke there is
no acceleration factor and NPSH minimum
depends on friction losses as calculated from
standard ow equations. With all viscous liquids
and in pilot plants and other places where
unusual numbers of fittings and valves are
used, the second condition that includes friction
losses should be considered. For water-like
liquids, the rst condition will dene the limiting
conguration.
For Static NPSH (Condition 1)
Available NPSH = Pa + Ph – Pv (must be equal
to or greater than minimum NPSH as listed under
Installation Instructions).
Required NPSH min = Sp. Gr. (0.0925) LpD
Dp
2
For Dynamic NPSH (Condition 2)
Available NPSH = Pa ± Ph – Pf Le (must be equal
to or greater than minimum NPSH as listed under
Installation Instructions).
D = Plunger Diameter (inches)
Dp = Pipe Diameter (inches)
Lp = Actual Length of suction pipe (feet)
Le = Equivalent length of suction pipe including
allowance for ttings (feet)
Pa = Ambient pressure above liquid (PSI)
Ph = Head of liquid column above (+) or below (–)
center line of plunger (PSI) equals Head in feet
x (0.435) (Sp.Gr.)
Pv = Vapor pressure of liquid (PSI)
Pf = Friction loss per foot of pipe calculated from
Reynold Number evaluation (PSI) (Use 3.2
times average velocity for calculating friction
losses when referring to a standard pipe losses
table)
Minimum NPSH = Minimum hydraulic pressure
at plunger (listed under Installation Instructions).
When operating the pump with a NPSH of less
than atmospheric pressure (negative suction head
or suction lift), special attention should be given to
keep the suction line strainer clean and prevent
other system conditions that might inadvertently
decrease the NPSH available.
NOTE:
Obtain our NPSH calculation software at
the Milton Roy website (miltonroy.com). If
assistance in determining NPSH is needed,
contact the Milton Roy Aftermarket Service
Department.

Milton Roy mRoy B Specifications

General

Brand	Milton Roy
Model	mRoy B
Category	Water Pump
Language	English