Selection of valve accessories — solenoid valve

What are the structural forms of three-way solenoid valve? For what occasion?
Three way solenoid valve can be divided into ordinary type, waterproof type, explosion-proof type and so on.
According to its action mode, it can be divided into direct acting type and pilot type. In the direct acting type, the coil pulls in the iron core to directly drive the stop valve to switch the gas path; in the pilot type, the coil pulls in the moving iron core to change the flow direction of elegant and popular air, and pushes the stop valve to switch the gas path through the compressed air.
According to its working state, it can be divided into two types: normally on type (open when power on, close when power off) and normally closed type (close when power on, open when power off).
The three-way solenoid valve is used in single acting pneumatic actuator and pneumatic diaphragm actuator to complete the automatic switching of air circuit to realize the opening and closing action of regulating valve. It is usually used in remote control, sequence control and interlocking system.
Why do the solenoid valves used in the interlock system always work in the normally energized state?
This is from the perspective of ensuring safety and reliability.
1. The interlocking system of petroleum and chemical plant is set up to ensure safety in production and prevent accidents, so the reliability of its sending message period and actuator is very high. The solenoid valve in the interlocking system doesn’t act at ordinary times, but only acts in case of accident. According to the working principle of the solenoid valve, the coil closes the moving iron core when it is powered on, and drives the valve parts to switch. When the power is off, the moving iron core and valve parts return to the original position by the action of the reset spring. If there is no power supply for a long time at ordinary times, due to rust, dirt invasion and other reasons, the moving iron core and valve parts may be stuck. In case of emergency power on, the coil will not be able to suck, and the guide finger will be out of action. If there is no power supply for a long time at ordinary times, due to the vibration of the solenoid valve, it can prevent jamming. In case of power failure due to accident, the switch can be carried out reliably by the action of return spring.
2. It is difficult to know whether the solenoid valve works normally when it is in power-off state. But usually in the power on state, once the solenoid valve itself failure, it can be checked out at any time, which is very important to ensure the reliability of the interlocking system.
3. In case of power failure, the solenoid valve can still operate reliably.
Due to the above reasons, the solenoid valve used in the interlocking system generally works under the state of constant power on, which is opposite to the situation described in the instruction manual of the solenoid valve. Therefore, the normally closed solenoid valve should be selected for the normally open situation, and the normally open solenoid valve should be selected for the normally closed situation.
What problems should be paid attention to when installing the three-way solenoid valve.
1. It should be installed vertically. The stop valve part of pilot solenoid valve should be in horizontal position.
2. Attention should be paid to the symbols of each nozzle, and do not touch it to prevent misoperation or accidents.
3. The power supply used shall meet the power requirements specified on the product name plate to prevent the coil from being burnt out.
4. The working gas source should be well purified.