Working principle of pneumatic control valve

The working principle of pneumatic control valve is simply achieved by compressed air, and in practical applications, it is of great significance to understand the working principle of the pneumatic valve.

Pneumatic control valve is one of the industrial process control instruments widely used in petroleum, chemical, power, metallurgical and other industrial enterprises. Usually by pneumatic actuators, valves, positioners and other connections, installation, debugging, the formation of pneumatic control valve.

Working principle of pneumatic control valve

Pneumatic control valve is driven by compressed air source to the cylinder as the actuator and valve positioner by means of electrical, converter, solenoid valve, position control valve and other accessories to drive the valve, switch or proportional regulator, receive to complete the flow pressure temperature and other parameters regulating pipeline control signal industrial automation control system. Pneumatic control valve is characterized by simple control, fast response, and intrinsically safe, do not need to take other measures to prevent explosion.

Pneumatic control valve action, gas split type and gas off type two. Air Open (Air to) is that when the air pressure on the membrane head increases, the valve moves to increase the opening direction. When the input pressure is limited, the valve is in full open state. Conversely, when the air pressure decreases, the valve moves in the closed direction and closes the valve without entering the air.

It is also called open type air valve closed fault type (Fail to Close FC). The Close to (Air) moves in the opposite direction to the air opening. When the air pressure increases, the valve moves in the closed direction; when the air pressure decreases or not, the valve opens or opens to the open. Sometimes it is also called FO to Open (Fail). The pneumatic opening or closing of a pneumatic control valve is usually accomplished by the positive and negative actions of the actuator and the different assembly methods of the valve state structure.

The choice of gas off and air off is based on the safety of process production. When the gas is cut off, is the valve in a closed position, safe or open position safe?

For example, the combustion control of a heating furnace is mounted on the fuel gas pipeline to control the fuel supply according to the temperature of the furnace or the temperature at which the material is heated at the outlet of the heater. At this time, it is advisable to use gas open valve safer, because once the gas supply stopped, the valve is closed, more open than the valve is more appropriate.

If the gas source is interrupted, the fuel valve is fully opened, which can cause excessive heating. And as a cooling water cooling heat exchange equipment of the hot material in the heat exchanger and the cooling water is cooled by heat exchange, regulating valve installed in the cooling water pipe, with the temperature of materials after heat exchange to control the cooling water in the gas supply interruption, the valve should be in a position to open more safely that should use air to close valve (FO).

Valve positioner

The valve positioner is the main control valve accessories, and pneumatic control valve is matched, it receives the output signal from the regulator, then its output signal to control the pneumatic valve, when the valve moves, the stem of the displacement and through the feedback mechanism to the valve positioner, valve position to the host through the electrical signal system.

Valve positioner according to its structure and working principle, can be divided into pneumatic valve positioner, electrical valve positioner and intelligent valve positioner.

The valve positioner control valve to increase the output power, reduce the transfer delay adjustment signal, speed up the movement of the valve stem can improve the linearity of the valve, the valve stem friction to overcome and eliminate the influence of unbalanced force, thus ensuring the correct positioning of the valve.

The actuator is divided into two parts: an executive mechanism, an electric actuator, and a straight stroke and an angular stroke. With automatic and manual opening and closing the valve plate, all kinds of wind.