Steam Valve Cv Calculator
Brought to you by ControlPix, your source for high quality, 3D, animated HVAC graphics.

for use with Tridium Niagara, Vykon, Staefa Talon, Distech EC-Net, Johnson Controls Facility Explorer FX FX-40,
Honeywell WEBsAX, Invensys Niagara Framework systems and many others.

Caveat Emptor: While we believe the calculations to be accurate,
the user bears the ultimate responsibility for proper valve sizing.
Use good engineering practices and check, check, check.

Calculate Flow, Pressure Drop, and Cv

Click on the button you want to calculate, after filling in the other parameters.

Flow (Lb / Hr)

Inlet (PSIG)

Pressure Drop (PSI)


The critical pressure drop is 45% of the absolute inlet pressure. = (Inlet gauge pressure + 14.7 PSI) x 0.45.

Increasing the pressure drop beyond critical does not result in more steam flow.

For steam inlet pressures of 12 PSIG or less, choose a pressure drop up to the inlet pressure.
80% of inlet gage pressure is recommended, and used in the "Find Best Drop" calculations.

For steam inlet pressures greater than approximately 12 PSIG, choose a pressure drop less than or equal to the critical pressure drop.

Note: After entering the steam line pressure, the "Find Best Drop" button chooses the higher of (80% of inlet pressure) or critical pressure drop.
The "best" pressure drop results in the best valve controllability. You can enter your own pressure drop value if your requirements are different.


If your calculated Cv does not exactly match what you have available, choose the valve with the next greater Cv.

E-mail us ! Let us know if you find this useful, and also if you have any comments for improvements.

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©2001 William C. Gausman