Knowledge expansion I

The pneumatic diaphragm control valve in the figure belongs to the air off type. Some people asked, why? First, look at the air inlet direction of the pneumatic film, which is a positive effect. Second, look at the installation direction of the spool, positive effect. The pneumatic diaphragm chamber is connected with the air source, and the diaphragm presses down the six spring covered by the diaphragm, so as to push the valve rod to move downward. The valve rod is connected with the valve core, and the valve core is installed in the positive direction, so the air source is the valve to move to the closed position. Therefore, it is called gas shut-off valve. When the gas supply is interrupted due to construction or corrosion of the gas pipe, the valve will reset under the reaction force of the spring, and the valve will be in the fully open position. How to use gas shut-off valve? How to use it is considered from the safety point of view, which is the necessary condition to select the gas on or off. For example: one of the core devices of the boiler is the steam drum. A regulating valve used in the water supply system must be air closed. Why? For example, if the gas source or power supply is suddenly interrupted, the furnace is still burning violently, continuously heating the water in the steam drum. If the gas is used to open the control valve and the energy is interrupted, the valve will be closed and the steam drum will be dry (dry burning) every minute without water inflow. This is very dangerous. It is impossible to deal with the fault of the control valve in a short time, which will lead to the boiler shutdown accident. Therefore, in order to avoid dry burning or even shutdown accident, the valve must be closed with gas. Although the energy is cut off and the control valve is in the full open position, the water is continuously fed into the drum, but it will not cause the drum to dry up. There is still time to deal with the control valve failure, so it is not necessary to shut down the boiler directly. Through the above examples, it is time to have a preliminary understanding of how to select the air on control valve and air off control valve!