solenoid valve in flue gas desulfurization of thermal power plant
Principle of solenoid box and its composition
In order to facilitate the following comparison between standard installation control mode and centralized control mode of solenoid valve box, the working principle of solenoid valve and pneumatic actuator used, as well as the actual composition and working characteristics of solenoid valve box are briefly described.
（1） solenoid valve working principle
The solenoid valve is composed of electrical components and mechanical parts. The electrical parts are composed of static iron core, moving iron core, coil, wiring base and protection circuit; the mechanical part is composed of valve body, slide valve core, slide valve sleeve, base, spring (for spring reset), etc. It can switch the position of valve core through the change of magnetic force when the coil is electrified or cut off, so as to achieve the purpose of switching or changing the direction of fluid. The solenoid valve used in safety interlock protection system mainly includes two position three-way, two position five-way and so on. Two position means that the valve core has two working positions, and three-way or five-way means that the valve has three or five interfaces.
（2） pneumatic actuator working principle
The pneumatic actuator is controlled by the solenoid valve. When the action is needed, the direction of compressed air inlet and outlet is changed through the power on and power-off of the solenoid valve to make the piston move, thus changing the rotation direction of the output shaft of the pneumatic actuator to control the opening and closing of the valve connected with it.
（3） Double acting pneumatic actuator
When the compressed air is input from port a, the left and right pistons move in the direction indicated by the arrow, the output shaft rotates anticlockwise, and the air on the side of the two pistons is discharged from port B. When the compressed air is input from port B, the left and right pistons move in the direction indicated by the arrow, the output shaft rotates clockwise, and the air on the side of the two pistons is discharged from Port A