The automatic sprinkler consists of assembly of a liquid filled glass bulb fitted in brass or bronze yoke with a deflector at outlet and threaded inlet connection.
The glass bulbs are rated for particular temperature, block the outlet orifice to pressurise the downside of the alarm valve to keep valve closed in normal condition. In case of fire the liquid inside glass bulb expands and shatters the glass bulb to open the orifice and water under pressure starts flowing in the form of spray.
In place of glass bulb fusible metallic string assembly is also used.
Sprinklers are available in various temperature rating and selected on the basis of the temperature of the surrounding where they are to be fixed.
The sprinkler system consist of water storage reservoir, a pump of suitable discharge capacity and pressure normally installed near reservoir and delivery mains taken up to the area under protection in the proper distribution of pipe mains and branches.
There is an isolating valve and a special valve (known as sprinkler alarm valve) on the delivery main near the area under protection. The valve is normally under closed position due to the pressure hold at down stream of the valve by sprinkler bulbs. The pipe branches are properly distributed over the area under protection to which the sprinklers are connected.
Under fire condition the sprinkler bulb burst as the rated temperature arrives and releases the water held by glass bulb. Due to the pressure difference at the seat of alarm valve causes to open the valve to provide water to the sprinkler. As the valve get open it gives alarm with gong connected to the system.
The sprinklers continuously spray water at the seat of fire till the isolating valve is manually closed and reset the alarm valve.