Wet rising mains are intended for use by the fire brigade or other trained personnel.
They are vertical mains fitted into staircase enclosures or other suitable positions, with outlet valves on each floor and connected to an automatic water supply.
Wet rising mains are designed to supply 1500 litres per minute for 45 minutes as a minimum.
The water supply consists of a tank with a minimum nominal size of 45m3 which is split across 2 compartments/tanks and 2 automatic fire pumps (duty and stand-by).
The tank has a breeching inlet fitted at ground level to enable the fire brigade to fill the wet riser tank remotely, it also must have an automatic infill valve from the towns' main to ensure the tank is maintained full at all times.
The tanks are fitted with an automatic warning system to allow the fire brigade to know at what level the tanks are to avoid tank becoming empty or overfilled.
To comply with the current British Standard BS9990 2015 the minimum outlet pressure required at each wet riser valve is 8 bars. Due to the height of the building and the pressures used, pressure regulating valves (PRV's) are fitted to the outlets at each floor.
In addition a permanent means of testing needs also to be provided this is usually done by means of a test drain which discharges either to a drain, sump or returned to the wet riser tank.
Buildings constructed prior to 2006 will have outlet pressures of 4 to 5 Bars. Changes to the British Standards in 2006 now recommend an outlet pressure of 8 Bars, this recommendation does not affect installations installed before this date.