Dry Pipe Water Sprinkler System
A Dry Pipe Sprinkler System is one in which pipes are filled with pressurized air or nitrogen, rather than water. This air holds a remote valve, known as a 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 releases. Water then enters the pipe, flowing through open sprinklers onto the fire.

Under Irish and European Design Codes for Automatic Sprinklers Systems it is possible to use and Alternate "Wet and Dry" Systems.

Dry pipe sprinkler systems provide automatic protection in locations where freezing is possible. Typical dry pipe installations include unheated warehouses and attics, outside exposed loading docks and within commercial freezers.

The alternate wet and dry system is used where the sprinkler pipes may be subjected to freezing temperatures at certain times of the year, when the system is used 'dry'. When freezing temperatures do not occur, the system is used 'wet'.

The sprinkler pipe work of a dry or alternate system is installed with a gradual fall to permit drainage of the system when it is changed from 'wet' to 'dry'. Drain valves at all low parts of the installation are opened periodically on 'dry' to allow drainage of any condensation.

Many people view dry pipe sprinklers as advantageous for protection in water sensitive areas. This perceived benefit is due to a fear that a physically damaged wet pipe system will leak while dry pipe systems will not. In these situations, however, dry pipe systems will generally not offer any advantage over wet pipe systems. Should impact damage happen, there will only be a mild discharge delay, i.e. 1 minute, while air in the piping is released before water flow.