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 carying 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.



In [1]:

    
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 = 1.582563779 meter / second
Velocity in 80 mm valve = 1.04907178712 meter / second
Minimum velocity = 1.02523019353 meter / second
Velocity in 60 mm valve = 1.61936609196 meter / second
Loss coefficient = 24.8796766231 dimensionless
Pressure drop = 13666.0409068 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.