Pre-action alarm valves are generally installed in places where water is needed to extinguish fire, but water spraying is not allowed unless it is caused by fire. Such as libraries, archives, museums, valuables storage rooms, computer rooms, etc.
principle of operation
1. Below the pre-action valve is the deluge valve, and above it is the wet alarm valve. In the standby state, the system side is filled with pressurized gas, and the lower deluge valve relies on the pressure chamber or diaphragm chamber to control the pressure on the water source side.
2. In case of fire, two independent smoke detectors form a logic alarm signal, and the logic controller sends a control signal to open the solenoid valve on the pre-action alarm valve group (or open the manual quick-open valve) to relieve the pressure in the pressure chamber.
When the fire water in the pipe network flows, the flow switch and the low pressure switch are triggered, and when the pressurized water enters the alarm pipeline, the pressure switch and the hydraulic alarm bell are triggered. At the same time, open the quick exhaust valve, and the whole system will be drained and filled with water within 1min or 2min.
3. After exhausting and flushing, the pre-action system is converted into a wet system. When the fire temperature reaches the design temperature of the hot-melt element of the nozzle, the nozzle element bursts, and then the fire is extinguished directly.