Dry Risers are normally installed in Low Rise buildings (those less than 23 M in height). The riser pipe is empty and does not have any water in them. In the event of a fire incident, water is pumped into the riser from Fire tenders using the Fire brigade inlets provided at the bottom of the riser.
Wet risers provided in high rise buildings (more than 23 M in height). In these systems, the riser pipe is always full of water, and is pressurized using gravity tanks, or dedicated fire pumps. Hence water is always available for fire fighting. Fire brigade inlets are also provided on wet riser systems, to provide water in case of failure of the system fire pumps.
Air Release valves are required in dry riser systems installed in buildings. When water is pumped into the riser through Fire Brigade inlets (using Fire Tender pumps), the air in the pipe should be released from the highest point in the piping to allow water to flow in (and prevent compression of the trapped air). Air release valves (installed at the top of the riser) allow the air to be released, but once water reaches the valve, it closes the valve, allowing build up of water pressure in the riser, and enabling fire fighters to use this water for fire fighting
In high rise buildings, the pressure will vary at the different floors due to the difference in head at the different levels. This can result in vast difference in pressure from top of the building to the bottom. To ensure that the same standard pressure is available from hydrant valves at all levels, different size orifice plates are required to be fitted at the inlet of the hydrant valve. The orifice size will depend on the level of the hydrant and the running pressure required from the hydrant.
Fire Hose Reels provide a first line of defence for building occupants in the event of fire. Like fire extinguishers, these are considered first aid appliances. Due to a low flow rate, there is no problem of jet reaction, and being simple in operation, hose reels can be safely used by occupants to fight small fires in buildings.
Vertical hose reels are standard fire fighting hose reels used in building applications. These are preferred in building applications due to low space requirement. The hose reel pipe is normally of ¾” to 1” diameter size, with 30 mtrs length.
Horizontal hose reels are larger (in width) as compared to vertical hose reels (and can thus accommodate longer lengths of hose), but have similar applications. As it is possible to mount larger diameter hoses (typically 1 to 1¼”), these are preferred in industrial fire fighting applications, and for use on Fire Tenders.