Introduction of pneumatic control valve

Pneumatic control valve uses compressed air as the power source, cylinder as the actuator, and drives the valve by means of electric valve positioner, converter, solenoid valve, retaining valve and other accessories to realize switching or proportional adjustment, receiving industry The control signals of the automatic control system are used to complete various process parameters such as regulating the flow, pressure and temperature of the pipeline medium. The characteristics of the pneumatic control valve are simple control, fast response, and intrinsic safety, no need to take additional explosion-proof measures.

The pneumatic regulating valve operates in two types: air opening type and air closing type. The air-opening type is when the air pressure on the diaphragm head increases, the valve moves in the direction of increasing opening, and when the upper limit of the input air pressure is reached, the valve is fully open. Conversely, when the air pressure is reduced, the valve moves in the closing direction, and when there is no input air, the valve is fully closed. Therefore, sometimes the gas-open valve is also called the fault-close type. The gas-closed action direction is exactly opposite to the air-open type. When the air pressure increases, the valve acts in the closing direction; when the air pressure is reduced or not, the valve is in the opening direction or fully open. Therefore, it is sometimes called fault open type. The air opening or closing of the pneumatic regulating valve is usually achieved by the different positive and negative actions of the actuator and the different assembly of the valve state structure.

The choice of gas-opening is based on the safety perspective of process production. When the air supply is cut off, is the control valve safe in the closed position or in the open position? For example, in the combustion control of a furnace, the regulating valve is installed on the fuel gas pipe to control the supply of fuel according to the temperature of the furnace or the temperature of the heated material at the outlet of the furnace. At this time, it is more safe to use the gas-opening valve, because once the gas source is stopped, the valve is closed more than the valve is fully open. If the air supply is interrupted and the fuel valve is fully open, there is a danger of excessive heating. Another example is a heat exchange device cooled by cooling water. The hot material is cooled by heat exchange with the cooling water in the heat exchanger. The regulating valve is installed on the cooling water pipe, and the temperature of the heat exchanged material is used to control the amount of cooling water. When the air supply is interrupted, it is safer to make the regulating valve in the open position. The gas-closed (ie FO) regulating valve should be used.