7.27 Sizing Control Valves for Liquid Service

Given 250 gpm of condensate from a pressurized condensate tank, is cooled from 225 deg F to 160 deg F in a heat exchanger, then pumped to a 50 psig heater.

The inlet and outlet pipe of the control valve is schedule 40, with no valves or fittings near the control valve. The system is located in a facility near sea level.

A single port globe style valve is to be added.

Find an appropriate size valve for the level control.

The valve options are 2”, 2.5”, 3”, or 4”; with Cvs of 41, 73, 114, and 175 respectively.

from fluids.units import *

rho = 60.998*u.lb/u.ft**3
mu = 0.39*u.cP
Psat = 4.75*u.psi
Pc = 3198*u.psi

Q = 250*u.gal/u.min
P1 = 80.6*u.psi
P2 = 70.8*u.psi

NPS, D_pipe, Do_pipe, t = nearest_pipe(NPS=4, schedule=40)

Cvs = [41*u.gal/u.min, 73*u.gal/u.min, 114*u.gal/u.min, 175*u.gal/u.min]
D_valves = [2*u.inch, 2.5*u.inch, 3.0*u.inch, 4*u.inch]

for d, Cv in zip(D_valves, Cvs):
    Kv = size_control_valve_l(rho=rho, Psat=Psat, Pc=Pc, mu=mu, P1=P1, P2=P2, Q=Q, D1=D_pipe, D2=D_pipe,
                             d=d, FL=0.9, Fd=1, allow_choked=True,
                             allow_laminar=True, full_output=False)
    Cv_calc = Kv_to_Cv(Kv)
    if Cv > Cv_calc:
        print('Minimum size is %s' %d)
        break
print('Calculated Cv is %s' %(Cv_calc))

Minimum size is 3.0 inch
Calculated Cv is 80.00778994084568 gallon / minute

Crane reports a Cv of 79.94. No iteration is required in this problem, except in the control valve sizing function itself.