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Calcimator

Control Valve Sizing Calculator

Cv from flow rate, pressure drop, and fluid properties.

Inputs

Results

Calculated Cv

44.72

Selected standard Cv

46

Oversize ratio1.03
Valve authority (N)0.5
Authority rating (0-2)2
Valve rangeability50
Min controllable flow (GPM)2
Port velocity (ft/s)8.9
Valve Type NameGlobe
How to Use This Calculator
  1. Enter Design flow (GPM), Valve pressure drop (psi), and Coil/circuit drop (psi).
  2. Set Specific gravity, Valve Type, and Globe (50:1 rangeability).
  3. Adjust Ball (200:1 rangeability), Butterfly (25:1, large flows) as needed.
  4. Review Calculated Cv and Selected standard Cv.
  5. Use Oversize ratio and Valve authority (N) to inform your decision.

How the result changes with Design flow (GPM)

Design flow (GPM)Calculated CvSelected standard Cv
10,0004,472.141,160
35,00015,652.481,160
65,00029,068.881,160
90,00040,249.221,160

What each input means

Design flow (GPM)
Design water flow rate through the valve in gallons per minute.
Valve pressure drop (psi)
Pressure drop across the control valve at design flow. Higher = better authority but more pump energy.
Coil/circuit drop (psi)
Pressure drop across the coil and piping circuit (excluding valve). Used for authority calculation.
Specific gravity
Fluid specific gravity relative to water. Water = 1.0, 30% glycol ≈ 1.04.
Valve Type
Select control valve type

What each result means

Calculated Cv
Required valve flow coefficient from the ISA sizing equation: Cv = Q × sqrt(SG / deltaP).
Selected standard Cv
Next available standard valve Cv size. Choose the smallest standard size >= calculated Cv.
Oversize ratio
Selected Cv / Calculated Cv. Should be 1.0-1.5; >2.0 indicates oversizing risk.
Valve authority (N)
Ratio of valve drop to total circuit drop. Target >= 0.5 for good control. < 0.3 = poor controllability.
Authority rating (0-2)
0 = Poor (<0.3), 1 = Fair (0.3-0.5), 2 = Good (>=0.5).
Valve rangeability
Turndown ratio (max/min controllable Cv) for the selected valve type.
Min controllable flow (GPM)
Minimum flow the valve can control based on its rangeability.
Port velocity (ft/s)
Approximate fluid velocity through the valve port. Keep < 12 ft/s to avoid erosion and noise.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Design flow (GPM) = 100, Valve pressure drop (psi) = 5, Coil/circuit drop (psi) = 5, Specific gravity = 1 = 5 input(s) provided
  2. Calculate Calculated Cv
    Calculated Cv = flowGpm * sqrt(specificGravity / valveDeltaPsi)
    44.72 = 44.72
  3. Calculate Selected standard Cv
    Selected standard Cv
    46 = 46
  4. Calculate Oversize ratio
    1.03 = 1.03
  5. Calculate Valve authority
    0.5 = 0.5

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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