The most common type of Maple Grove fire protection system in use is the water sprinkler system, with the most popular being the wet pipe system. Wet pipe systems are filled completely with water up to the sprinkler heads, which, when activated, has water immediately available to douse the fire.
In areas where there is a danger of freezing, however, a dry pipe system is used. Areas that are more likely to have a dry pipe system include unheated warehouses, parking garages and cold storage plants. Dry pipe system do not allow water to be admitted to any portion of the pipe that could be exposed to freezing temperatures.
All piping that could be exposed to freezing temperatures is pressurized with compressed air or nitrogen, and this pressurization is done from the sprinkler heads back to the non-freezing area. A check valve will allow water to flow in the direction of the sprinkler heads, but it is held back by the gas pressure in the low temperature exposed fire protection area.
A sprinkler head will open when it senses the heat from a fire, allowing the gas to escape, lowering the pressure and allowing water to flow out. There is some delay before the water actually reaches the sprinkler head because it must purge out all gas to get to the sprinkler head. The fire code calls for systems to be designed so that water is available in less than a minute.
