Pulsafeeder PULSAR Shadow Series, Инструкция по установке, эксплуатации и обслуживанию

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31
10.2 System Backpressure
The system backpressure must exceed the suction pressure by at least 5 psi (0.35 bar)
in order to prevent flowthrough, however it must not exceed the rated discharge
pressure of the pump. Flowthrough can be defined as the process liquid flowing from a
higher pressure to a lower pressure (downhill pumping), which results in a flow output
greater than the pumps calibrated capacity, failure and undesired flow at pump
shutdown. If the system backpressure is not at least 5 psi (0.35 bar) greater than the
suction pressure, a backpressure valve must be installed in the discharge piping. To
calculate the total system backpressure use Equation 3 or 4.
Equation 3. For fluid viscosity below 50 centipoise.
P P
+ )
d C
RGQ
L
( =
P
H P
2
1
D
T
±
Equation 4. For fluid viscosity at or above 50 centipoise.
P P
+ )
d C
Q
L
( + )
d C
RGQ
L
( =
P
H P
2
4
2
D
2
2
1
D
T
±
µ
NOMENCLATURE
NPSH
R
Net positive suction head required, [psi, bar]
NPSH
A
Net positive suction head available, [psi, bar]
P
A
Pressure at the surface of the liquid being pumped (atmospheric or
supply tank blanket pressure) [psia, bar(a)]
P
H
Head pressure above (+) or below (-) the pump centerline, [psi, bar]
P
V
Absolute vapor pressure at pumping temperature of the process liquid at
pump inlet, [psia, bar(a)]
L
S
Length of suction piping (actual, not equivalent), [ft, m]
R Pump stroking rate, strokes/min [spm]
G Specific gravity of process liquid, [unitless]
Q Pump average flow rate, [gph, lph]
d Internal pipe diameter, [inches, mm]
C
1
,C
2
Numeric constants used in Equations 1- 4
μ
Viscosity of process liquid at pumping temperature, centipoise [cp]
L
D
Length of discharge piping (actual, not equivalent), [ft, m]
P
P
System discharge pressure, [psig, bar(g)]
P
T
Pump discharge pressure at the discharge port, [psig, bar(g)]