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Calcimator

Control Valve Cv Sizing Calculator

Size control valves per ISA/IEC 60534 for liquid or gas service. Calculate required Cv, check for choked flow, and select nearest standard valve size.

Inputs

Results

Required Cv

22.36

Nearest standard Cv

30

Pressure drop ΔP (psi)20
Choked flow? (1=yes, 0=no)0
Rangeability (selected/required)1.34
Pressure drop ratio x (ΔP/P₁)0.2
Critical drop ratio xT0.7
FL0.84
How to Use This Calculator
  1. Enter Service type (0=liquid, 1=gas), Flow rate (GPM or SCFH), and Inlet pressure P₁ (psia).
  2. Set Outlet pressure P₂ (psia), Specific gravity, and Temperature (°F).
  3. Adjust Critical pressure drop ratio xT, Piping geometry factor Fp as needed.
  4. Review Required Cv and Nearest standard Cv.
  5. Use Pressure drop ΔP (psi) and Choked flow? (1=yes, 0=no) to inform your decision.

How the result changes with Inlet pressure P₁ (psia)

Inlet pressure P₁ (psia)Required CvNearest standard Cv
1,0013.785
3,5012.023
6,5001.482
9,0001.262

What each input means

Service type (0=liquid, 1=gas)
0 = Liquid (GPM), 1 = Gas (SCFH).
Flow rate (GPM or SCFH)
Volumetric flow: GPM for liquid, SCFH (std cubic feet/hr) for gas.
Inlet pressure P₁ (psia)
Upstream pressure at valve inlet (absolute).
Outlet pressure P₂ (psia)
Downstream pressure at valve outlet (absolute).
Specific gravity
Relative to water (liquid) or air (gas) at standard conditions.
Temperature (°F)
Fluid temperature (primarily affects gas Cv calculation).
Critical pressure drop ratio xT
From valve manufacturer. Globe ≈ 0.7, ball ≈ 0.55, butterfly ≈ 0.5.
Piping geometry factor Fp
1.0 for line-size valve; < 1.0 for reduced-port or with reducers.

What each result means

Required Cv
Calculated valve flow coefficient needed for the specified conditions.
Nearest standard Cv
Next available standard valve Cv size.
Pressure drop ΔP (psi)
Pressure drop across the valve.
Choked flow? (1=yes, 0=no)
Whether flow is choked (limited) at these conditions.
Rangeability (selected/required)
Ratio of selected Cv to required Cv. Should be > 1 and ideally < 3–4.
Pressure drop ratio x (ΔP/P₁)
Actual pressure drop ratio.
Critical drop ratio xT
Pressure drop ratio at which flow becomes choked.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Service type (0=liquid, 1=gas) = 0, Flow rate (GPM or SCFH) = 100, Inlet pressure P₁ (psia) = 100, Outlet pressure P₂ (psia) = 80 = 8 input(s) provided
  2. Calculate Required Cv
    Required Cv = Cv
    22.361 = 22.361
  3. Calculate Nearest standard Cv
    Nearest standard Cv = standardCvs[standardCvs.length - 1]
    30 = 30
  4. Calculate Pressure drop ΔP
    Pressure drop ΔP = max(0.01, p1 - p2)
    20 = 20
  5. Calculate Choked flow?
    0 = 0

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