Fire hydrant

The user (most likely a fire department) 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 kilopascals (51 psi); 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.

[4] If a fire hydrant is opened or closed too quickly, a water hammer can occur and damage nearby pipes and equipment.

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 opening to control individual outputs and allow for changing equipment connections without turning off the flow to other outlets.

It is good practice to install valves on all outlets 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.

In 1896, during a terrible heatwave in New York City, the Commissioner of Public Works ordered the opening of the fire hydrants to provide relief to the population.

[5] Today some US communities provide low flow sprinkler heads to enable residents to use the hydrants to cool off during hot weather, while gaining some control on water usage.

To prevent casual use or misuse, the hydrant requires special tools to be opened, usually a large wrench with a pentagonal socket.

Such vandalism can also reduce municipal water pressure and impair firefighters' efforts to extinguish fires.

In most areas of the United States, contractors who need temporary water may purchase permits to use hydrants.

Often sewer maintenance trucks need water to flush out sewerage lines and fill their tanks on site from a hydrant.

Automatic flushing devices are often attached to hydrants to maintain chlorination levels in areas of low usage.

In countries including Japan, the UK, Ukraine, Russia or Spain hydrants are accessible under a heavy metal cover.

In the United States, the AWWA and NFPA recommend hydrants be colored chrome yellow[6] for rapid identification apart from the bonnet and nozzle caps which should be coded according to their available flow.

In Germany, the Netherlands, Spain, the UK, and many other countries, most hydrants are located below ground and are reached by a riser, which provides the connections for the hoses.

In areas of the United States without winter snow cover, blue reflectors embedded in the street are used to allow rapid identification of hydrants at night.

In rural areas tall narrow posts painted with visible colours such as red are attached to the hydrants to allow them to be found during heavy snowfall periods.

If it is not a common fire hydrant type then another identification may be used, for example "300 m³" would point to a cistern usable to pump water from.

In East Asia (China, Japan and South Korea) and former Socialist countries of Eastern Europe, there are two types of fire hydrants, of which one is on the public ground and the other inside a building.

They are big, rectangular boxes that also provide alarms (sirens), a fire extinguisher and, at certain times, emergency kits.

Without extending the height, the wrenches to remove caps would not clear and the break flanges for traffic models would not be located correctly in case they were hit.

A dry hydrant is usually an unpressurized, permanently installed pipe that has one end below the water level of a lake or pond.

Before piped mains supplies, water for firefighting had to be kept in buckets and cauldrons ready for use by 'bucket-brigades' or brought with a horse-drawn fire-pump.

[13] When cast iron pipes replaced the wood, permanent underground access points were included for the fire fighters.

Some countries provide access covers to these points, while others attach fixed above-ground hydrants – the first cast iron ones were patented in 1801 by Frederick Graff, then chief-engineer of the Philadelphia Water Works.