A wet pipe system is the most common type of fire sprinkler system, in which the sprinkler pipes are constantly charged with water under pressure.
For this reason, it is only suitable for use where there is no danger of frost, i.e. in climates where freezing never occurs or in buildings which are constantly heated during cold periods. Wet-pipe systems should not be considered when ambient temperatures can fall below 4°C (40°F).
The layout of the controlling valves of a typical wet system is shown and it includes the alarm valve, the combined drain and test valve, test valve, pressure gauges and alarm motor isolating valve, strainer, alarm motor and gong.
This type of system is the easiest to design and relatively straightforward to maintain. Wet-pipe systems always contain water under pressure and utilise a series of closed sprinkler heads.
When a fire occurs and produces enough heat to activate one or more sprinklers, the water is discharged immediately onto the fire. A Wet-pipe system should be the first choice of specifiers and designers alike, as they are inherently more reliable and less costly to maintain.