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In your reservoir, get fluid surface pressure: Psurface.
Get the distance between the pump and liquid surface: Z. If the tank is above the pump, multiply this value by -1.
Obtain the vapor pressure for the system's temperature: Pvapor. Also, its density is ρ. Note g represents gravity.
Calculate all friction loss in the suction pipe: Hloss.
Solve: ((Psurface - Pvapor)/ρ × g) - Z - Hloss, and you will have NPSH available.
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