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Cv Flow Calculator

Created by Marcelina Wiśniewska
Reviewed by Dominik Czernia, PhD and Rijk de Wet
Last updated: Jun 14, 2023


If you came across our Cv flow calculator, you might be a professional looking for clues on how to select an appropriately sized valve for your project, or a student in search of the Cv calculation formula. Perhaps you need to convert Cv to flow rate. Whatever the case may be, look no further!

With this tool, youIn this article you will learn the definition of Cv flow, what the Cv flow coefficient is, and how to calculate it for a valve using the Cv equation.

Cv flow coefficient definition

The valve flow coefficient measures the capacity of a valve to let fluids pass through it. Technically, the definition of the Cv flow coefficient is: the volume of water at 60°F (in US gallons) that will flow through a valve per minute with a pressure drop of 1 psi across the valve.

If the coefficient of a particular valve is 1, then 1 US gallon of water will pass through it per minute, given that the pressure drop is equal to 1 psi. Clearly, the Cv valve coefficient changes depending on stem travel (how far the valve is open) — when fully opened, the Cv value is at its highest, meaning that the most liquid per minute can pass through it at this setting.

Now that we've defined Cv conceptually, let's see how to calculate it with the Cv flow formula!

Cv calculation formula

Before exploring how to calculate Cv for a valve, let's explain the variables that we will need for the Cv flow formula:

  • Specific gravity SGSG (also known as relative density) measures the density of a liquid compared to the density of water at 4 °C, or 39.2 °F. See our specific gravity calculator to learn more about this topic.
  • Flow rate QQ measures the volume of a liquid that passes through a given cross-sectional area in a given time. Our flow rate calculator explains this concept in more detail.
  • The pressure drop ΔP\Delta P at a given valve is defined as the difference between the inlet pressure and the outlet pressure and is dependent on the flow. This information should typically be provided by the manufacturer for a specific valve model. If you are able to measure the inlet and outlet pressure you can input that information in the advanced mode of our calculator.

Now that we understand the relevant variables, let's take a look at the Cv equation behind our Cv flow calculator:

Cv=Q×SGΔPC_v = Q\times\sqrt{\frac{SG}{\Delta P}}

All we need to do in order to obtain the flow coefficient is to divide the specific gravity SGSG of the liquid (1 for water) by the pressure drop ΔP{\Delta P}, take the square root of the result and multiply it by the flow rate QQ. Or plug in the values into the Cv flow coefficient calculator and let it do the work for you. Remember, you can always use our tool in reverse and convert Cv to flow rate instead.

Importance of the flow coefficient

Different valve types exist and depending on their size and design, they are represented by different valve coefficients. Now that you now how to use our Cv flow calculator, you can apply this knowledge to select the right product for your project.

Knowing how to calculate the Cv for a valve is important for the following reasons:

  • It helps you understand the effect that different factors have on the pressure in your system and make more informed decisions.
  • It saves costs. Thanks to our flow coefficient calculator you don't have to worry about overpaying for a valve that is too big for your needs.
  • It prevents damage. Selecting a valve too small could lead to a pressure buildup and result in damages to your system.

If you don't want to take the risk of hand-calculating Cv, you can always use our Cv flow calculator.

Marcelina Wiśniewska
Specific gravity
Liquid (medium)
Water
Specific gravity
Cᵥ flow
Flow rate
US gal/min
Pressure drop
psi
Valve flow coefficient (Cᵥ)
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