The flow characteristic of a valve is the relationship between the relative flow of the medium flowing through the regulating valve and its opening under the condition that the pressure difference at both ends of the valve remains constant. Flow characteristics are an important technical indicator and parameter of the regulating valve. It is of great significance to make the correct selection in the application process of the regulating valve.

The flow characteristic of the valve can be defined as: the relationship between the relative flow of the controlled medium flowing through the valve and the relative opening (relative displacement) of the valve is called the flow characteristic of the regulating valve. Generally speaking, it is divided into four types: linear, equal percentage (logarithmic), parabola and fast opening! The specific description and advantages are as follows:

First, the linear characteristic refers to the linear relationship between the relative flow and the relative opening of the valve, that is, the flow change time constant caused by the unit opening change. The relative stroke of the linear characteristic is in a linear relationship with the relative flow. The flow change caused by the change of unit stroke is constant. When the flow is large, the relative value of the flow changes little, and when the flow is small, the relative value of the flow changes greatly.

Second, the equal percentage characteristic (logarithm) means that the change in relative flow caused by the change in unit opening is proportional to the relative flow at that point, that is, the amplification factor of the regulating valve is variable, and it increases with the increase in relative flow. The relative stroke and relative flow of the equal percentage characteristic are not in a linear relationship. The change in flow caused by the change in unit stroke at each point in the stroke is proportional to the flow at this point, and the percentage of flow change is equal. Therefore, its advantage is that when the flow is small, the flow change is small, and when the flow is large, the flow change is large, that is, it has the same adjustment accuracy at different openings.

Third, the parabola characteristic means that the change in relative flow caused by the change in unit relative opening is proportional to the square root of the relative flow value at this point. The flow changes proportionally according to the square of the stroke, and generally has the intermediate characteristics of linear and equal percentage characteristics.

Fourth, the fast opening flow characteristic means that there is a large flow when the opening is small. As the opening increases, the flow can quickly reach the maximum. After that, the flow changes very little when the opening is increased, so it is called a fast opening characteristic.

The flow characteristics of diaphragm valves are close to quick opening characteristics, the flow characteristics of butterfly valves are close to equal percentage characteristics, the flow characteristics of gate valves are linear characteristics, and the flow characteristics of ball valves are linear in the middle opening and closing stages, and equal percentage characteristics when the opening is in the middle.

In general, ball valves and butterfly valves are usually not used for regulation. If they are used for regulation, they only play a regulatory role when the opening is very small. Generally speaking, they can be classified as quick opening type. Most of the valves that are really used for regulation are basically stop valves. The valve heads are processed into parabolic cones, spheres, etc., and different curve characteristics are used. Generally speaking, percentage characteristics are used more for regulation.