The Valve Flow Factor Conversion (Metric to U.S.) equation converts a valve's Metric Flow Factor (K_V) to the U.S. Flow Factor (C_V).

INSTRUCTIONS: Choose units and enter the following:

• (K_V) Metric Flow Factor

Description

Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is subdivided into hydraulics using a liquid such as mineral oil or water, and pneumatics using a gas such as air or other gases. Compressed-air and water-pressure systems were once used to transmit power from a central source to industrial users over extended geographic areas; fluid power systems today are usually within a single building or mobile machine.

Fluid power systems perform work by a pressurized fluid bearing directly on a piston in a cylinder or in a fluid motor. A fluid cylinder produces a force resulting in linear motion, whereas a fluid motor produces torque resulting in rotary motion. Within a fluid power system, cylinders and motors (also called actuators) do the desired work. Control components such as valves regulate the system.

The flow factor or coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice, valve or other assembly and the corresponding flow rate.

In more practical terms, the flow coefficient C_v is the volume (in US gallons) of water at 60° F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

The use of the flow coefficient offers a standard method of comparing valve capacities and sizing valves for specific applications that is widely accepted by industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases and steam as follows:

Coefficient of discharge is the ratio of actual flow rate to theoretical discharge.

For gas flow in a pneumatic system the C_v for the same assembly can be used with a more complex equation.^[1][2] Absolute pressures (psia) must be used for gas rather than simply differential pressure.

For air flow at room temperature, when the outlet pressure is less than 1/2 the absolute inlet pressure, the flow becomes quite simple (although it reaches sonic velocity internally). With C_v = 1.0 and 200 psia inlet pressure the flow is 100 standard cubic feet per minute (scfm). The flow is proportional to the absolute inlet pressure so that the flow in scfm would equal the C_v flow coefficient if the inlet pressure were reduced to 2 psia and the outlet were connected to a vacuum with less than 1 psi absolute pressure (1.0 scfm when C_v = 1.0, 2 psia input).

The metric equivalent flow factor (K_v; commonly used in Europe and Asia) is calculated similarly, but the rate of flow is expressed in units of cubic meters per hour, and the pressure in bar.

Related Equations

Industrial Fluid Equations Collection

References

This description was obtained from wikipedia.