7.32 NPSH Available Calculation

Given that a pump is located 30 feet above sea level, has a NPSHr of 20’ at a flow rate of 400 gpm, and is fed by a tank of 60 deg F water with a surface pressure of 5 psig and a liquid level 25’ below the suction of the pump.

The head losses in the suction pipeline are 6’.

Find the NPSH available and compare it to the NPSHr. A NPSHr margin ratio is required.

from fluids.units import *
rho = 62.364*u.lb/u.ft**3
P_tank = 5*u.psi + 1*u.atm
Psat = 0.256*u.psi
H_tank = 5*u.foot
H_pipe = 30*u.foot
dH = H_pipe - H_tank

head_loss = 6*u.foot

NPSHa = ((P_tank-Psat)/rho/u.gravity) - dH - head_loss
(NPSHa).to(u.foot)

13.887316780096477 foot

The NPSHa is beneath the NPSHr. The requested pressure can be calculated as follows:

20*u.foot*1.3

26.0 foot