Control valve is an automatic control system commonly used in the actuator, is the end of the automatic control of the main control components, direct control of the measured medium traffic. The control valve is composed of an actuator and an adjustment mechanism, which receives the control mark of the regulator or the attempt machine to corrupt the flow of the controlled medium so that the parameter is protected within the condition of the condition, so as to achieve the automation through the control. In the automatic control scale, the control process is safe depends on whether the control valve can accurately move, so that the process of control for the material energy and flow does change. Therefore, according to the different needs of the choice of different control valve. The choice of a reliable control valve is the key issue in piping planning and the key to ensuring the safe operation of the system.

(1) adjust the valve type selection

The valve body type of the control valve is the most important problem in the selection of the control valve. Before selecting the valve, the media, process terms and parameters of the control process should be elucidated to clarify the system requirements for the control valve, according to the data collected to confirm the type of valve to be used. In the detailed selection, you can discuss from the following aspects:

① spool demeanor structure? Mainly based on the selected flow characteristics and non-compliance and other factors to consider;

② wear resistance? When the fluid medium is a high concentration of abrasive particles containing the suspension, the valve core, seat joint surface every time the city closed by the tension. So the flow of the valve to be smooth, the inside of the valve to be strong;

③ corrosion-resistant? Because the media is corrosive, can meet the regulation of the output of the case, although the choice of simple structure of the valve;

④ medium temperature, pressure? When the medium temperature, pressure and change the big, should take the spool and valve seat material by the temperature, pressure changes in small valves;

⑤ avoid flashing and cavitation? Flash and cavitation only in the liquid medium. In the actual production process, the flash and cavitation not only the calculation of the flow coefficient, but also the formation of shaking and noise, so that the service life of the valve shorter, so the choice of the valve should prevent the valve flash and cavitation.

(2) control valve actuator selection

① consider the implementation of the agency's transmission performance? Actuator regardless of what type, its output force is used to overcome the load of the test (mainly refers to the unbalanced and unbalanced moments, friction, sealing force, gravity and other related The role of force). Therefore, in order to make the valve normally accident, equipped with the executive body to be able to produce more than the output force to overcome the various resistance to ensure a high degree of sealing and valve opening.

② consider the use of the implementation of the agency requirements? After the implementation of the executive force to determine the output, according to the use of environmental requirements, select the response of the implementing agencies. For example, on the scene with explosion-proof requirements, should use the pneumatic actuator, and the junction box for the explosion-proof type, not the choice of electric actuator. If there is no explosion-proof requirements, the pneumatic, electric actuators can be used, but from the energy-saving considerations, should try to use electric actuators. For the hydraulic actuator, although the use of less than pneumatic, electric actuator widely, but it has a high precision adjustment, fast and smooth action characteristics, so in exceptional circumstances, in order to achieve better adjustment will also choose. Finally, consider the implementation of the agency's reliability, economy, select the action smooth, light weight, the appearance of the United States, simple structure, easy maintenance of the implementing agencies.