Pulsafeeder Pulsar Shadow - Manual (Page 47)

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Table 2. Unit sets and constant values for use in NPSH Equations.
Variable
Units Set
English Metric
NPSH psi bar
P psia
A
bar(a)
P psi
H
bar
P psia
V
bar(a)
L feet
S
meters
R strokes/min strokes/min
G no units no units
Q gallons/hr liters/hr
d inches millimeters
µ centipoise centipoise
L feet
D
Meters
P psi
T
bar
P psi
P
bar
V feet/sec
P
meters/sec
C 24,600
1
640
C 45,700
2
1.84
C 46.8
3
0.91
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.)
All reciprocating metering pumps also require that a minimum absolute pressure and minimum suction
head (MSH), be maintained at the pump inlet throughout the pumping cycle to ensure a stable hydraulic
system and proper pump operation. The sum of the NPSH
A
and the vapor pressure (P
V
) must be greater
than the values shown in Table 3.
Table 3. Minimum values for the sum of NPSH
A
and vapor pressure. (MSH)
MSH PULSAR PULSAR*
English, (psia) 5 7.5
Metric, (bar(a)) 0.35 0.53
* PULSAR Pump with PULSAlarm leak detection diaphragm.