A fire hydrant is a water supply point. It serves a s a reservoir where water is tapped during fire fighting. It can be placed inside or outside a building, parking area, industrial area, mine, roadside, and designed to instantly provide the water required by fire fighters to extinguish a fire.
Types of Fire Hydrants
The dry hydrants, aka the standpipe, are commonly used by firefighters as the main water supply in rural areas where the municipal water system is a luxury and can’t be easily accessible. Typically, an unpressured, permanently installed pipe, the dry hydrant is well below the water level of a lake or pond at one end, usually with a strainer to prevent debris or foreign objects from entering the pipe.
The other end of the pipe, however, is located on the surface of the ground with a hard sleeve connector on it. A pumper fire engine drafts water from the lake or pond, when needed, with a primer by vacuuming the air out of the dry hydrant as well as the hard sleeve and fire engine pump.
Dry barrel fire hydrant needs to have a valve release to let water in. It has one or more valve openings above the ground line and, under normal operating conditions, the entire interior of the hydrant is subjected to water pressure at all times.
The wet barrel hydrant, with aboveground shut-off valves, holds no water in the barrel when not in use. With the valve of each outlet operating independently, this type of hydrant has an advantage over its dry barrel counterpart due to easy access to the aboveground mechanical parts for maintenance and adjustments, which of course turns out to be more economical.
Despite all the advantages, the Achilles’ heel of the wet barrel hydrants is freezing, and that’s why they are installed in areas with warm climates.
What Are Fire Hydrants Used For
Hydrants are devices for extracting water from pipelines and water distribution systems. In the event of a fire, a hydrant can assure fast water supply. The connections to the pipes are tapped with so-called hydrant wrenches and hydrant standpipes and are further connected to the fire trucks.
Components of The Fire Hydrant
|• Fire Fighting Pumps & Accessories
|• Landing Valves
|• Hose Reel
|• Branch Pipes & Nozzles
|• Fire Brigade Connections
|• Wiring & Instrumentations
|• Maintenance Valves
Installation Requirement For Fire Hydrants
A. Fire hydrants shall be a minimum of 50 feet away from a building or structure, unless as determined by the Fire Chief; a longer minimum distance is needed for the safety of firemen and fire vehicles using the hydrant.
B. Buildings having a required flow of 2,500 or more gallons per minute shall be served by fire hydrants with mains which loop around the building or complex of buildings and reconnect or extend to another grid system.
C. Buildings having a required fire flow of less than 2,500 gallons per minute may be permitted to have hydrants on one side of the building only.
D. Location of fire hydrants shall be subject to approval of the Fire Chief, considering such factors as utilities, topography, and building location.
Fire Hydrant Pressure
Operation Of The Fire Hydrant
The user attaches a hose to the fire hydrant, then opens a valve on the hydrant to provide a powerful flow of water, on the order of 350 kPa (50 pounds per square inch gauge (psig); this pressure varies according to region and depends on various factors including the size and location of the attached water main). This user can attach this hose to a fire engine, which can use a powerful pump to boost the water pressure and possibly split it into multiple streams.
One may connect the hose with a threaded connection, instantaneous “quick connector” or a Storz connector. A user should take care not to open or close a fire hydrant too quickly, as this can cause a water hammer, which can damage nearby pipes and equipment. The water inside a charged hose line causes it to be very heavy and high water pressure causes it to be stiff and unable to make a tight turn while pressurized. When a fire hydrant is unobstructed, this is not a problem, as there is enough room to adequately position the hose.
Most fire hydrant valves are not designed to throttle the water flow; they are designed to be operated full-on or full-off. The valving arrangement of most dry-barrel hydrants is for the drain valve to be open at anything other than full operation. Usage at partial-opening can consequently result in considerable flow directly into the soil surrounding the hydrant, which, over time, can cause severe scouring.
Gate or butterfly valves can be installed directly onto the hydrant orifices to control individual outputs and allow for changing equipment connections without turning off the flow to other orifices. These valves can be up to 12 inches in diameter to accommodate the large central “steamer” orifices on many US hydrants. It is good practice to install valves on all orifices before using a hydrant as the protective caps are unreliable and can cause major injury if they fail.
When operating a hydrant, a firefighter typically wears appropriate personal protective equipment, such as gloves and a helmet with face shield worn. High-pressure water coursing through a potentially aging and corroding hydrant could cause a failure, injuring the firefighter operating the hydrant or bystanders.
In most jurisdictions it is illegal to park a car within a certain distance of a fire hydrant. In North America the distances are commonly 3 to 5 m or 10 to 15 ft, often indicated by yellow or red paint on the curb. The rationale behind these laws is that hydrants need to be visible and accessible in an emergency.
When Does NFPA Require Fire Hydrant Testing?
Regular fire hydrant testing ensures the ability to provide water at an acceptable pressure and flow rate for public health and firefighting operations. Most jurisdictions also require hydrant flow tests to design fire sprinkler systems for commercial or residential structures.
The 2019 edition of NFPA 291: Recommended Practice for Fire Flow Testing and Marking of Hydrants (4.1.3) recommends that fire hydrants should maintain a residual pressure of 20 psi (pounds per square inch), or 1.4 bar, for effective firefighting, as well as to prevent backflow that could contaminate the public water supply.
NFPA 291 stipulates hydrant flow tests every five years to ensure that changing conditions in the piping and system demands won’t impede hydrants’ ability to deliver water.