|In a dry-pipe system, sprinklers are attached to pipes that contain pressurized air. When heat activates the sprinklers, the air pressure is reduced, allowing the dry-pipe valve to open (or trip) and water to flow to the sprinklers.
Dry-pipe systems are usually used only when temperatures are not high enough to prevent freezing (Below 40 deg. F).
Since dry systems have a slower response time, they should be converted to wet-pipe systems as soon as sufficient heat becomes available.
In situations where only a few sections lack heat, it is recommended to use a combination of dry and wet-pipe systems.