Regulating valve type and selection

The regulating valve, also known as the control valve , changes the fluid flow by means of a power operation by accepting a control signal output from the regulating control unit. The regulating valve is generally composed of an actuator and a valve. If the power used by the actuator is matched, the regulating valve can be divided into three types: pneumatic regulating valve, electric regulating valve and hydraulic regulating valve, that is, pneumatic regulating valve with compressed air as power source and electric power source. Regulating valve, electrohydraulic regulating valve powered by liquid medium (such as oil), in addition to its function and characteristics, hydraulic control valve, solenoid valve, electronic, intelligent, fieldbus type regulating valve Wait.

Valve body type selection of regulating valve
There are many types of valve bodies for regulating valves. Commonly used valve bodies are straight-through single-seat, straight-through two-seat, angular, diaphragm, small flow, three-way, eccentric rotation, butterfly, sleeve, and spherical. In the specific choice, you can make the following considerations:
(1) Spool shape structure
Mainly based on factors such as selected flow characteristics and imbalance forces.
(2) Wear resistance
When the fluid medium is a suspension containing a high concentration of abrasive particles, the internal material of the valve is tough.
(3) Corrosion resistance
Due to the corrosive nature of the media, try to choose a simple valve.
(4) Temperature and pressure of the medium
When the temperature and pressure of the medium are high and the change is large, the valve and the material of the valve seat should be selected to be small in temperature and pressure.
(5) Prevent flashing and cavitation
Flashing and cavitation are only produced in liquid media. In the actual production process, flashing and cavitation will form vibration and noise, shortening the service life of the valve, so the valve should be prevented from flashing and cavitation when selecting the valve.

Control valve actuator selection
In order for the regulating valve to work properly, the actuator must be equipped with sufficient output force to ensure a high degree of sealing and opening of the valve.
For double-acting pneumatic, hydraulic, and electric actuators, there is generally no return spring. The magnitude of the force is independent of its direction of travel. Therefore, the key to selecting an actuator is to clarify the large output force of the Zui and the rotational torque of the motor. For a single-acting pneumatic actuator, the output force is related to the opening of the valve. The force appearing on the regulating valve will also affect the motion characteristics. Therefore, it is required to establish a force balance across the opening range of the regulating valve.

Determination of the type of actuator
After determining the output force of the actuator, select the corresponding actuator according to the requirements of the process environment. For explosion-proof requirements on site, pneumatic actuators should be used. In terms of energy saving, electric actuators should be selected as much as possible. If the adjustment accuracy is high, the hydraulic actuator can be selected. Such as the speed regulation of the power plant transparent machine, the temperature regulation control of the catalytic converter of the refinery.

The mode of action of the regulating valve
The mode of action of the regulating valve is only when the pneumatic actuator is selected, and its action mode is formed by the combination of the positive and negative action of the actuator and the positive and negative action of the valve. There are 4 kinds of combination forms, namely, positive (gas-off type), positive and negative (air-open type), anyway (air-open type), anti-reverse (air-closed type), and the regulating valve formed by these four combinations has a gas function. Both open and closed. The choice of the mode of action of the regulating valve is mainly considered from three aspects: a) process production safety; b) medium characteristics; c) product quality assurance, economic loss