Control valve is used to adjust the medium flow, pressure and level. According to adjust the position of the signal, the valve automatically control the opening, so as to achieve the media flow, pressure and liquid level adjustment. Regulating valve sub-electric control valve, pneumatic control valve and hydraulic control valve and other electric control valve is the process control of industrial automation, an important unit of execution instrumentation. As the degree of automation in the industrial field is getting higher and higher, it is being used more and more in various industrial fields. Compared with the traditional pneumatic control valve has obvious advantages: energy saving (consumption of electricity only during work), environmental protection (non-carbon emissions), quick and easy installation (without complex pneumatic piping and pump workstations). Pneumatic control valve is the compressed air as the power source to the cylinder as the actuator, and with the help of electrical valve positioners, converters, solenoid valves, retention valves and other accessories to drive the valve to achieve the switch or the proportion of regulation, the receiving industry Automatic control system to complete the control signal to adjust the pipeline media flow, pressure, temperature and other process parameters. Pneumatic control valves are characterized by simple control, fast response, and intrinsically safe, eliminating the need for additional explosion-proof measures. The history of the automatic control valve dates back to self-operated pressure regulators, which consist of a ball valve with weight rod, Something is used to balance the force on the spool to some degree of regulation. Another early self-regulating regulator was in the form of a pressure-balanced regulator. The pressure of the process is connected to the thin film gas chamber of the spring membrane pressure regulating valve by a pipeline. Whether it is a pressure reducing valve, a pressure regulator or a differential pressure regulator, the flow capacity is created from the change of such a base valve. Cv is one of the main parameters for selecting a control valve. Flow capacity is defined as: When the control valve is fully open, the pressure across the valve is 0.1MPa, the fluid density of 1g / cm3 hourly flow control valve flow number, known as the flow capacity, also known as flow coefficient, To Cv, the unit is t / h, liquid Cv value calculated according to the following formula. According to the flow capacity Cv value of the size of the table, you can determine the nominal diameter of the control valve DN flow control valve flow characteristics is the pressure drop at both ends of the valve to maintain a constant condition, the medium flow through the control valve relative to its open The relationship between degrees. Regulating valve flow characteristics of linear characteristics, such as percentage characteristics and parabolic characteristics of three. The significance of the three kinds of fluency features are as follows: (1) Parabolic characteristics The flow rate changes proportionally according to the two sides of the stroke, and generally has the intermediate characteristic of linearity and equal percentage characteristics. (2) Linearity (Linearity) Relativeness and linearity of linearity are linear. Changes in unit stroke caused by changes in the flow is unchanged. When the flow rate is large, the relative value of the flow rate changes little, and when the flow rate is small, the relative value of the flow rate changes greatly. (3) Equal Percentage (Logarithmic) Equal Percentage The relative and relative flow rates do not have a linear relationship. The change in flow per unit of stroke at each point of travel is directly proportional to the flow rate at that point. The percentage change in flow rate Is equal. So it has the advantage of small flow, small changes in traffic, traffic flow, the flow changes, that is, in different degrees, with the same regulation accuracy. From the analysis of the above three characteristics can be seen, in terms of its regulatory performance, with equal percentage characteristics for the best, stable regulation, good regulation performance. The parabolic characteristics than the linear properties of the regulatory performance is good, according to the different requirements of the occasion, select any one of the flow characteristics. More keyword search: Regulating valve