What should be noted when selecting control valves? Precautions for selecting control valves

The regulating valve, also known as the control valve, is a final control component in the field of industrial automation process control. It accepts the control signal output by the regulating control unit and uses power operation to change process parameters such as medium flow, pressure, temperature, and liquid level.

A control valve is generally composed of an actuator and a valve. According to the stroke characteristics, control valves can be classified into linear stroke and angular stroke.

According to the power used by the actuator they are equipped with, they can be classified into three types: pneumatic control valves, electric control valves and hydraulic control valves.

According to their functions and characteristics, they can be classified into three types: linear characteristics, equal percentage characteristics and parabolic characteristics.

The control valve is suitable for air, water, steam, various corrosive media, slurry, oil products and other media. So, what should be noted when choosing a control valve? Now let's take a look together at the precautions for selecting control valves.

What should be noted when selecting a control valve?

It is unreasonable to directly select the control valve according to the diameter of the connecting pipe. The regulating quality of a valve has nothing to do with the flow rate or pipe diameter of the connecting pipe. The regulating quality of a valve is only related to the resistance and flow rate of the water. Once the system equipment is determined, theoretically, there is only one ideal diameter of valve suitable for the system, and there will not be multiple options.

2. The diameter of the control valve should not be too small. If the selected valve diameter is too small, on the one hand, it will increase the resistance of the system. On the other hand, it may even lead to the situation where the system still fails to meet the set capacity requirements when the valve diameter is fully opened, resulting in serious consequences. On the other hand, the valve will need to provide a large pressure difference through the system to maintain sufficient flow, which increases the load on the pump. The valve is prone to damage and has a significant impact on its service life.

3. The diameter of the control valve should not be too large. If the selected valve diameter is too large, it not only increases the project cost but also causes the valve to frequently operate within a low percentage range. This will lead to a decrease in regulation accuracy, a deterioration in control performance, and make the system prone to shock and oscillation.

4. To ensure the quality of system control, the best approach is to select a valve diameter within the allowable range of the system that can achieve a larger pressure drop, so that the change in pressure drop during the operation of the valve is as small as possible. The higher the percentage of pressure drop in the fully open state of the valve to the total pump pressure, the smaller the relative change value of the valve pressure drop, and the closer the installation characteristics of the valve are to its inherent characteristics.

5. The regulating valve in the control system should operate under a constant pressure drop as much as possible. Whether the valve matches the coil depends on its inherent characteristics and flow factor, and these valve parameters depend on a constant valve pressure drop.