The CV curve of a valve, also known as the flow characteristic curve, illustrates the relationship between the valve’s flow capacity (CV) and the valve’s opening position or percentage of valve opening (typically represented as a percentage of full opening). CV stands for flow coefficient, which is a measure of the valve’s capacity to pass fluid. This curve is crucial in understanding how a valve regulates flow under different conditions.
The CV curve typically starts from zero flow when the valve is fully closed and rises as the valve opens. However, the rate at which the curve rises can vary depending on the type of valve and its design. There are different types of flow characteristics:
- Linear: In a linear characteristic valve, the flow rate increases linearly with the valve’s opening. This means that if you graph the flow rate against the valve opening percentage, you’ll get a straight line.
- Equal percentage: In this type of characteristic, equal increments of valve opening result in equal percentage changes in flow rate. This is a common type of characteristic for control valves because it provides better control over a wide range of flow rates.
- Quick opening: A valve with a quick opening characteristic allows a large flow rate to pass through with a small change in valve position. This type of characteristic is often used in on-off valves where rapid full opening is desired.
The shape of the CV curve influences how the valve behaves in different applications. Engineers select valves with appropriate flow characteristics based on the requirements of the system they are designing or operating. Understanding the CV curve helps in proper valve selection and efficient control of fluid flow in various industrial processes.