The working principle of pneumatic control valve is to use compressed air as the power source and cylinder as the actuator, and drive the valve with the help of electric valve positioner, torque converter, solenoid valve, holding valve and other accessories to realize on-off or proportional regulation. The control signal of the automatic control system is used to adjust the pipeline medium: flow, pressure, temperature and other process parameters. It is characterized by simple control, fast response, intrinsic safety and no need to take additional explosion-proof measures.
Pneumatic control valve is one of the industrial process control instruments widely used in petroleum, chemical, electric power, metallurgy and other industrial enterprises. It is usually a combination instrument for connecting, installing and adjusting pneumatic actuators and regulating valves.
Pressure reducing valve usually consists of connecting, installing and adjusting pneumatic actuator and pressure reducing valve. Pneumatic actuators are divided into single acting and double acting. There is a return spring in the single acting actuator and no return spring in the double acting actuator. When the single acting driver loses its origin or suddenly fails, it can automatically return to the switching state set at the initial stage of the valve.
The action of air pressure regulating valve has two types: air open type and air closed type. When the air pressure on the membrane head of the air open type increases, the valve will act in the direction of increasing the opening. When the upper limit of the input air pressure is reached, the valve will become fully open. On the contrary, when the air pressure decreases, the valve moves in the closing direction. When the air is not input, the valve is fully closed. Therefore, air open valve is sometimes called fault closed valve. The action direction of exhaust type is opposite to that of exhaust type. When the air pressure increases, the valve acts in the closing direction; When the air pressure drops or disappears, until the valve is opened or fully opened. Sometimes referred to as fail on type. The air opening or closing of air pressure regulating valve is usually realized by the positive and negative action of actuator and different assembly methods of valve state structure.
The valve positioner is the main accessory of the control valve and is used in combination with the pneumatic control valve. Receive the output signal of the regulator and control the air pressure regulating valve through the output signal. When the regulating valve works, the displacement of the valve stem is fed back to the valve positioner through the mechanical device, and the position of the valve is transmitted to the upper system through the electrical signal. According to its structural form and working principle, valve positioner can be divided into air valve positioner, electrical valve positioner and intelligent valve positioner. The valve positioner can increase the output of the regulating valve, reduce the transmission delay of the regulating signal, accelerate the moving speed of the valve stem, improve the linearity of the valve stem, overcome the friction of the valve stem, eliminate the influence of unbalanced force, and ensure the correct positioning of the regulating valve.
