A dry pipe system is one in which pipes are filled with pressurised air or nitrogen, rather than water. The air pressure holds the Dry-pipe valve in a closed position.
Located in a heated space, the dry-pipe valve prevents water from entering the pipe until a fire causes one or more sprinklers to operate. Once this happens, the air escapes and the dry pipe valve opens. Water then enters the pipe network flowing through the open sprinklers onto the fire.
Dry pipe sprinkler systems provide automatic protection in locations where freezing is possible and are typically used in unheated warehouses, exposed loading docks and within commercial freezers.
The sprinkler pipe work of a dry system is installed with a gradual fall to permit drainage of the system. Drain valves at all low parts of the installation are opened periodically to allow drainage of any condensation.
Many people view dry pipe sprinklers as advantageous for protection in areas sensitive to water. This perceived benefit is due to a fear that a damaged wet pipe system will leak while dry pipe systems will not. In these situations, dry pipe systems will generally not offer any advantage over wet pipe systems. Should impact damage happen, there will only be a short discharge delay, i.e. 60 seconds, while air in the piping is released before water flows.