A valve’s flow characteristic or CV curve is a graphical representation that illustrates the relationship between the flow rate through the valve and the valve’s opening percentage (from fully closed to fully open). The CV curve helps engineers and technicians understand how a valve will perform in a specific application and is an essential factor in valve selection and system design.
The term CV stands for “flow coefficient” or “valve flow coefficient” and is a standardized value used to express the flow capacity of a valve. The higher the CV value, the greater the flow capacity of the valve.
There are three common types of valve flow characteristics:
- Linear: A linear CV curve has a direct proportional relationship between the flow rate and the valve opening percentage. In this case, when the valve opening increases by a certain percentage, the flow rate increases by the same percentage. Linear valves are typically used in applications where precise flow control is required.
- Equal percentage: An equal percentage CV curve has a logarithmic relationship between the flow rate and the valve opening percentage. This means that the flow rate increases exponentially as the valve opening increases. The equal percentage characteristic is often used in processes where a wide range of flow rates and precise control is needed, such as temperature or pressure control applications.
- Quick opening: A quick opening CV curve has a relationship where the flow rate increases rapidly with a small increase in the valve opening percentage and then levels off as the valve continues to open. Quick opening valves are used in applications where a fast response is needed, such as safety shutoffs or on/off control applications.
Understanding the CV curve of a valve is essential for selecting the right valve for a specific application and ensuring optimal system performance. The chosen valve should match the desired flow characteristic for the intended use, providing efficient and precise control of the flow rate within the system.