There are four types of sprinkler systems:
Wet Pipe System
A sprinkler system employing automatic sprinklers attached to a piping system containing water and connected to a water supply so that water discharges immediately from sprinklers opened by heat from a fire.
Dry Pipe System
A sprinkler system employing automatic sprinklers attached to a piping system containing air or nitrogen under pressure, the release of which (from the open sprinklers) permits the water pressure to open a valve known as a dry pipe valve. The water then flows into the piping system and out the opened sprinklers.
A sprinkler system employing automatic sprinklers attached to a piping system containing air that may or may not be under pressure, with a supplemental detection system installed in the same areas as the sprinklers. Actuation of the detection system opens the pre-action valve, which permits water to be discharged from sprinklers that are open.
A sprinkler system employing open sprinklers attached to a piping system connected to water supply through a valve that is opened by the operation of a detection system installed in the same area as the sprinklers. When the valve opens, water flows into the piping system and discharges water from all sprinklers attached thereto.
Automatic sprinkler systems are installed to protect property and the occupants in the building. These systems are particularly effective for life safety because they give warning of the existence of fire and at the same time apply water to the burning area. While the downward force of the water may lower the smoke level in a room where the fire is burning, the sprinklers also serve to cool the room and reduce the immediate threat to personnel.