Switching valve (forced Valve) is a pneumatic switching valve installed on the hot end of switching heat exchanger (or cooler. The switch of the switch valve is controlled by the signal compressed air through the solenoid valve. According to the different functions in the process, there are air, sewage and nitrogen switching valve, pure nitrogen suppression valve, sewage and nitrogen three-way valve, etc. It can be divided into vertical and horizontal structures. Vertical switch valve can be divided into air open type and Air closed type. Air open type means that when the signal compressed air is cut off, the valve flap can open automatically depending on its own weight; otherwise, it is gas closed type. The selection of gas on and off is determined by the safety of the device. Nitrogen switch valve uses air open type, air switch valve uses Air closed type.
Since the movement of the switch valve is controlled by the solenoid valve, in addition to the choice of open gas and closed gas to prevent the gas source failure from bringing harm, we should also pay attention to the coordination between the state of the solenoid valve and the state of the switch valve, so as not to endanger the safety of the equipment when the power supply fails. Now it is explained as follows:
1) sewage nitrogen switching valve. When the four-way solenoid valve has power, the switch valve is closed (figure 127b ). When the power is out, the switch valve is open (figure 127a ). And when the power supply loses power and the air source loses voltage, it can also be turned on by itself. So as to ensure that when the fault occurs, the gas in the upper tower can be emptied through the cooler, which will not cause overpressure.
2) air switch valve. When the four-way solenoid valve has power, open the switch valve (figure 128b ). When power is out, the switch valve is closed (figure 128a ). When the power failure of the control power supply loses power, the switch valve closes; when the pressure loss of the control air source failure, the switch valve closes by its own weight to ensure that the raw material air does not enter the air separation tower when the failure occurs.
3) dirty nitrogen (pure nitrogen) three-way switch valve. The four-way solenoid valve has electricity, and the three-way switch valve is in the discharge position (figure 129b); the four-way solenoid valve loses power, and the three-way switch valve is in the emptying position (figure 129a ). When the power failure loses power, the three-way switch valve is in the emptying position; when the gas source failure loses pressure, the three-way switch valve can be in the emptying position by its own weight.
