If the flame is extinguished due to accidental reasons, the electromotive force generated by the thermocouple disappears or nearly disappears. The suction of the solenoid valve also disappears or greatly weakens, the armature is released under the action of the spring, the rubber block installed on its head blocks the gas hole in the gas valve, and the gas valve is closed.
Because the electromotive force generated by the thermocouple is relatively weak (only a few millivolts) and the current is relatively small (only tens of milliamps), the suction of the safety solenoid valve coil is limited. Therefore, at the moment of ignition, the shaft of the gas valve must be pressed to give an external force to the armature along the axial direction, so that the armature can be absorbed.
The new national standard stipulates that the opening time of safety solenoid valve is ≤ 15s, but generally controlled by manufacturers within 3 ~ 5S. The release time of safety solenoid valve is within 60s according to the national standard, but generally controlled by the manufacturer within 10 ~ 20s.
There is also a so-called "zero second start" ignition device, which mainly adopts a safety solenoid valve with two coils, and a newly added coil is connected to the delay circuit. During ignition, the delay circuit generates a current to keep the solenoid valve in the closed state for several seconds. In this way, even if the user immediately releases his hand, the flame will not go out. And usually rely on another coil for safety protection.
The installation position of the thermocouple is also very important, so that the flame can be well baked to the head of the thermocouple during combustion. Otherwise, the thermoelectric EMF generated by the thermocouple is not enough, the suction of the safety solenoid valve coil is too small, and the armature cannot be absorbed. The distance between the thermocouple head and the fire cover is generally 3 ~ 4mm.