Pulsafeeder Pulsar Shadow - Manual (Page 38)

10. APPENDIX I Piping Calculations
10.1 Suction Head Requirements
All reciprocating metering pumps require a net positive suction head (NPSH
R
). The NPSH
R
for PULSAR
Shadow ® pumps is 5 psi (0.35 bar). The NPSH
R
is defined as the pressure required above the absolute
vapor pressure of the process fluid at the pumping temperature. This pressure is required at the suction
port of the pump throughout the entire pump stroking cycle in order to prevent cavitation of the process
fluid within the reagent head. Satisfying the NPSH
R
is required to assure metering accuracy.
The net positive suction head available (NPSH
A
) must be greater than the NPSH
R
. The NPSH
A
of any
given system is calculated as follows:
Equation 1. For fluid viscosity below 50 centipoise.
Equation 2. For fluid viscosity at or above 50 centipoise.
The variables used in Equations 1 through 4 must be in the units shown in the table below for the
constants listed below to be used correctly.
Units Set
Variable
English Metric
NPSH psi bar
P
A
psia bar(a)
P
H
psi bar
P
V
psia bar(a)
L
S
feet meters
R strokes/min strokes/min
G no units no units
Q gallons/hr liters/hr
d inches millimeters
µ centipoise centipoise
L
D
feet Meters
P
T
psi bar
P
P
psi bar
V
P
feet/sec meters/sec
C
1
24,600 640
C
2
45,700 1.84
Note: If piping sizes vary throughout the
suction line, different additive values may be
used for the pressure losses attributed to the
liquid’s acceleration and deceleration. Use the
last term of Equation 1 or 2 as many times as
needed in the equation to adjust for different
lengths of different pipe diameters in the
suction line. (Everything but the pipe length
and diameter will stay the same in the
equation.)
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