What is the working principle of the pneumatic pneumatic - valve

Pneumatic pneumatic - valve action points gas open type and close type two kinds. Then the working principle of the pneumatic pneumatic control valve is what? Gas is when film head type air pressure increases, the valve to increase the opening direction of the movement, when to input pressure limit, the valve is in the fully open position. On the other hand, when the air pressure is reduced, the valve moves in the direction of closing, when no input air, the valve full close. So sometimes gas type valve is also called fault closed type ( 失败关闭FC) 。 Type gas shut movement direction is just the reverse of gas drive type. When the air pressure increases, the direction of the valve to close actions; Air pressure decreases or not, or fully open valve to open direction. So sometimes called fault open type ( 无法打开FO) 。 Pneumatic pneumatic control valve of gas or gas close, usually by positive and negative effects of the actuator and valve structure of different assembly way. Gas-off choice is according to the process of production safety perspective to consider. When gas source to cut off the pneumatic control valve is in the closed position safety or open position? Gas open change for gas closed type or closed type gas for gas open, such as pneumatic - valve equipped with smart valve positioner, can easy to switch from the each other at the scene. But there are some occasions, when a failure does not want the valve is in full open or close position, operation is not allowed, but hope that a failure to keep before the expiration of the original location. At this moment, can take some other measures, such as using the position valve or set special air cylinder storage facilities to ensure that the accident. For example, a heating furnace combustion control, pneumatic control valve installed in the fuel pipe road, according to the temperature of the furnace or the temperature of the heated material in furnace exit to control the supply of fuel. At this time, appropriate chooses gas valve is safer, because once the air stop supply, valve in the closed is more suitable than the valve is fully open. If air supply interruption, fuel valve fully open, can make the heat excess risk.