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4.4.2.5 Sample NPSHA calculation

Figure 4.6: Diagram for NPSH calculation

Liquid to be pumped Water at 140 ~ F
Flowrate required through the pump 340 gpm
Calculated suction line size 6 inches
NPSHA = Hs + Ha- Hvp- Ht
Static Head (Hs)
The vertical distance from the elevation of the free surface of the
liquid in the supply tank to the horizontal centerline of the impeller. = 45ft.
Surface Pressure (Ha)
Absolute head on the surface of the liquid in the supply tank.
= Surface pressure x 2.31 / s.g.
= 14.7 psia x 2.31 / 0.985 = 34.474 ft.
Vapor Pressure (Hvp)
Vapor pressure expressed in terms of feet of head.
= 2.889 x 2.31 / 0.985 - 6.775 ft.
Friction Loss (Hs)
Piping Losses based on a flow rate of 340 gpm
(from Friction Loss Tables for 6 inch line) - 0.806 ft per 100 feet length
Losses in 25 ft - 0.806 x 25 / 100 - 0.2 feet
Valves and Fittings Losses based on a Flow Rate of 340 gpm
(from Resistance Coefficient Tables and Friction Loss Tables)
Velocity Head (V2/2g) = 0.222
K-Factor on Flanged Gate Valve = 0.11
K-Factor on Flanged Standard Elbow = 0.29
Friction Loss in 2 Valves = 0.222x0.11x2 = 0.049 feet
Friction Loss in 2 Elbows = 0.222 x 0.29 x 2 = 0.129 feet
Total Friction Losses = 0.378 feet

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