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12.
APPENDIX II
12.1
Piping Calculations
All reciprocating metering pumps require a net positive suction head (NPIPR). Refer to Table 1 for
the (NPIPR) required for PULSAPRO pump models. The NPIPR 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 to
prevent cavitation of the process fluid within the reagent head. The NPIPR is one of the
requirements necessary to assure metering accuracy.
Table 1
The net positive suction head available (NPIPA) must be greater than the NPIPR. The NPIPA of
any given system is calculated as follows for comparison to the NPIPR as shown in Table 1.
Equation # 1 – For fluid viscosity below 50 centipoises
Equation # 2 – For fluid viscosity above 50 centipoises
Refer to Section 12.3 Nomenclature, for the definitions of variables used in the equations above; follow the
units shown in Table 3B for the constants listed to be used correctly.
IF PIPING SIZES VARY THROUGHOUT THE SUCTION LINE, DIFFERENT ADDITIVE VALUES MAY BE
USED FOR 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 NPSHa and the vapor pressure (pv) must be greater than the values
shown in table 2.
MSP
PULSAPRO
English, (psia)
7.5
Metric, (bar(a))
0.53
Table 2 -
Minimum values for the sum of NPIPA and vapor pressure. (MSP)
NPIPR
PULSAPRO
English (psi)
5
Metric (bar)
0.34
