If suction head is excessive in a centrifugal pump, flow rate
and pressure may be reduced
Or suction function may be weakened due to occurrence of cavitation.
Therefore, net positive
Suction head in the conditions where pump is installed be higher
than the required NPSH
Value of the pump.
Calculation
of Net Positive Suction Head
hsv
= Pa/r ± Hs - Hl - Pvp/r
hsv
: Net Positive Suction Head[m]
Pa
: Pressure of suction watet level (Absolute pressure) [kg/㎡]
Hs : Ssuction[m] in case of svction(-), and in case of inlet
pressure(+)
Hl : Suction los head[m]
Pvp : Vapor pressure at the water temperature[kg/㎡]
r : Fluid weight of unit volume[kg/㎥]
1.
Water temperature 25℃ suction head -6m when loss in the suction
pipe is ignored
Pa = 10,330kg/㎡ Pvp : 323kg/㎡
Hl = 0, r = 1000kg/㎥
Hsv = 10.33-6-0.323=4.01m
2.
in case that water temperature is 60℃
r = 983kg/㎥ Pvp = 2031kg/㎡
hsv = 10.52-6-2.07=2.45m
3.
Hs = 4m 압입, water temperature 100℃
r
= 958kg/㎥ Pcp = 10,330kg/㎡
hsv
= 10.78+4-10.78=4m
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