The regulating valve is also known as the control valve, which changes the fluid flow by receiving the control signal output by the regulating control unit and using power operation.The regulating valve is generally composed of an actuator and a valve.According to the power used by the actuator, the control valve can be divided into three types: pneumatic control valve, electric control valve, and hydraulic control valve, namely pneumatic control valve with compressed air as the power source, and electric control valve with electricity as the power source. Regulating valve, an electro-hydraulic regulating valve powered by the pressure of a liquid medium (such as oil, etc.). In addition, according to its functions and characteristics, there are hydraulic control valves, solenoid valves, electronic, intelligent, and fieldbus control valves. Wait.
Selection of the valve body type of the regulating valve
There are many types of valve bodies for regulating valves. Common types of valve bodies include straight-through single-seat, straight-through double-seat, angle, diaphragm, small flow, three-way, eccentric rotation, butterfly, sleeve, spherical, etc.In the specific selection, the following considerations can be made:
(1) Spool shape and structure
Mainly based on the selected flow characteristics and unbalanced force and other factors.
(2) Wear resistance
When the fluid medium is a suspension containing a high concentration of abrasive particles, the internal material of the valve should be hard.
(3) Corrosion resistance
As the medium is corrosive, try to choose a valve with a simple structure.
(4) The temperature and pressure of the medium
When the temperature and pressure of the medium are high and the changes are large, the valve core and valve seat materials should be selected with small changes in temperature and pressure.
(5) Prevent flashing and cavitation
Flashing and cavitation only occur in liquid media.In the actual production process, flashing and cavitation will cause vibration and noise, which will shorten the service life of the valve. Therefore, when selecting the valve, prevent the valve from flashing and cavitation.
The choice of regulating valve actuator
In order for the regulating valve to work normally, the equipped actuator must be able to produce enough output force to ensure a high degree of sealing and valve opening.
For double-acting pneumatic, hydraulic, and electric actuators, there is generally no return spring.The magnitude of the force has nothing to do with its running direction. Therefore, the key to selecting an actuator is to understand the maximum output force and the rotating torque of the motor.For single-acting pneumatic actuators, the output force is related to the opening of the valve, and the force appearing on the regulating valve will also affect the motion characteristics, so it is required to establish a force balance across the opening range of the regulating valve.
Determination of the type of implementing agency
After determining the output power 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.From the perspective of energy saving, electric actuators should be used as much as possible.If the adjustment accuracy is high, a hydraulic actuator can be selected.Such as the speed adjustment of the transparent machine of the power plant, the temperature adjustment control of the catalytic device reactor of the oil refinery, etc.
Selection of the mode of action of the regulating valve
The mode of action of the regulating valve is only available when the pneumatic actuator is selected, and its mode of action is formed by the combination of the positive and negative effects of the actuator and the positive and negative effects of the valve.There are 4 types of combinations, namely, positive (air-to-close type), positive and negative (air-to-open type), anyway (air-to-open type), and reverse (air-to-close type). The regulating valve action mode formed by these four combinations has air There are two types: on and off.Regarding the selection of the mode of action of the regulating valve, there are three main considerations: a) process production safety; b) characteristics of the medium; c) ensuring product quality with minimal economic loss
