7.5 Lift Check Valves

A lift check valve of type globe (with a wing-guided disc) is added to a 80 mm Schedule 40 horizontal pipe carrying water at a flow rate of 300 L/min.

Calculate the check valve size, and pressure drop. The disc should be fully lifted at the specified flow.

from fluids.units import *
from math import *
Q = 300*u.L/u.min
D_80 = 77.9*u.mm

rho = 998.2*u.kg/u.m**3
# Try: schedule 40, 80 mm valve
D_60 = 62.7*u.mm
v_lift = v_lift_valve_Crane(rho=rho, D1=D_80, D2=D_80, style='lift check straight')
print('Minimum velocity = %s' %v_lift)

v =  Q/(pi/4*D_80**2)
print('Velocity in 80 mm valve = %s' %v.to_base_units())

# v is lower than the lift velocity; try the 60 mm valve
v_lift = v_lift_valve_Crane(rho=rho, D1=D_60, D2=D_80, style='lift check straight')
print('Minimum velocity = %s' %v_lift)

v =  Q/(pi/4*D_60**2)
print('Velocity in 60 mm valve = %s' %v.to_base_units())
# The desired velocity is close enough

fd = 0.017 # given, 80 mm pipe upstream
K2 = K_lift_check_valve_Crane(D_60, D_80, fd=fd, angled=False)
print('Loss coefficient = %s'%K2)
v_pipe = Q/(pi/4*D_80**2)

dP = 0.5*rho*v_pipe**2*K2
print('Pressure drop = %s' %dP.to(u.Pa))

Minimum velocity = 1.5825637790011153 meter / second
Velocity in 80 mm valve = 1.0490717871198245 meter / second
Minimum velocity = 1.0252301935349282 meter / second
Velocity in 60 mm valve = 1.6193660919636594 meter / second
Loss coefficient = 24.87967662305315 dimensionless
Pressure drop = 13666.040906803597 pascal

The values calculated in the example are K2 = 26.3 and pressure drop = 14450 Pa. Interestingly, the formula for minimum lift velocity used in their example does not use the ratio of diameters as the formula in their appendix shows. Otherwise the examples match.