Enter the rate of flow, the specific gravity of the fluid, and the pressure drop across the valve to calculate the flow coefficient.

CV Flow Formula

The following formula is used to calculate the CV flow coefficient. 

Cv = Q * Sqrt ( SG / P )
  • Where CV is the coefficient of flow
  • Q is the flow rate
  • SG is the specific gravity of the fluid inflow
  • P is the pressure drop across the valve the fluid is moving through

To calculate the coefficient of flow, multiply the flow rate by the square root of the ratio of specific gravity to the pressure drop.

CV Flow Definition

A CV flow, more commonly known as the coefficient of flow, is a measure of the ability of a fluid to flow rate a valve at a certain pressure drop.

CV Flow Example

How to calculate CV flow coefficient?

First, determine the rate of flow. This is typically expressed in gallons per minute (GPM). For this example, the flow is determined to be 50 GPM.

Next, determine the specific gravity of the fluid. To make things simple, this example will assume water at 4C which has a specific gravity of 1.

Next, determine the pressure drop across the valve. In this problem, the pressure drop is found to be 5 psi.

Finally, using the formula, calculate the flow coefficient.

CV = 50* Sqrt ( 1/5) = 22.360.

FAQ

What is specific gravity and how does it affect the flow coefficient?

Specific gravity (SG) is a measure of the density of a fluid compared to the density of water at 4°C (39°F), which is set as 1. The specific gravity of the fluid influences the flow coefficient (CV) because it affects the fluid’s resistance to flow under a given pressure drop. A higher specific gravity means the fluid is denser, and thus, more force (or a higher pressure drop) is required to move it at the same rate as a less dense fluid.

Can the CV flow coefficient be used for gases, or is it only for liquids?

The CV flow coefficient can be used for both gases and liquids. However, the calculation and considerations might slightly differ due to the compressibility of gases. For gases, factors such as temperature and pressure must be taken into account to accurately calculate the flow coefficient.

How does the pressure drop across a valve affect the flow rate of a fluid?

The pressure drop across a valve is a measure of the resistance or friction that the fluid encounters as it moves through the valve. A higher pressure drop indicates more resistance, which can reduce the flow rate of the fluid. Conversely, a lower pressure drop means less resistance, allowing for a higher flow rate. The flow coefficient (CV) quantifies this relationship by indicating how much flow can pass through a valve at a specific pressure drop.

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