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Fire hydrant

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A fire hydrant is a critical component of active fire protection. It serves as a connection point where firefighters can tap into a municipal water supply.

Downtown Charlottesville fire hydrant
Downtown Charlottesville fire hydrant

These devices allow for a powerful and immediate flow of water during emergencies. While they are primarily used to fight fires, they are also part of the broader water distribution system. Hydrants come in many different shapes and styles depending on where they are located. Some sit above ground as pillars, while others remain hidden under metal covers in the street.

Operating a hydrant requires precision and speed. A firefighter typically attaches a hose to the hydrant using a threaded connection, an instantaneous quick connector, or a Storz connector.

Hydrantandcb
Hydrantandcb

Once connected, the user opens a valve to release the water. This water flows with significant pressure, which depends on the size and location of the water main. To increase this force, the hose can be attached to a fire engine. The engine uses a powerful pump to boost the pressure or split it into multiple streams. Firefighters must be careful not to open or close the valve too quickly. Doing so can cause a water hammer, which is a pressure surge that can damage pipes and equipment.

There are two primary types of hydrants: dry-barrel and wet-barrel. In regions with freezing temperatures, engineers use dry-barrel hydrants.

Cross-sectional illustration of a typical dry-barrel hydrant
Cross-sectional illustration of a typical dry-barrel hydrant

In this design, the main valve is located below the frost line. The vertical body, or barrel, remains dry because a drain valve opens when the main valve is closed. This allows water to drain away so the hydrant does not freeze and crack. In warmer climates, wet-barrel hydrants are more common. These hydrants keep water in the barrel at all times. Wet-barrel models allow operators to control each outlet individually, providing more flexibility during use.

History shows that hydrant technology has changed significantly over time. Underground hydrants have been utilized in Europe and Asia since at least the 18th century. However, the above-ground pillar-type hydrants used today were a 19th-century invention. In the United States, many hydrants feature a large central outlet called a "steamer" connection. This name is a historical leftover from when these outlets supplied steam-powered water pumps. Today, firefighters undergo intensive training in fire academies to master these connections. They are often expected to connect a fire engine to a hydrant in less than one minute to save critical time.

Visual identification is vital for emergency responders, so hydrants are often color-coded. In the United States, the NFPA 291 provides guidelines for marking hydrants to indicate available water flow. The color of the nozzle caps tells a firefighter how many gallons per minute (gpm) the hydrant can provide. For example, Class AA hydrants provide more than 1500 gpm and have light blue caps. Class A hydrants provide 1000 to 1499 gpm and have green caps. Class B hydrants offer 500 to 999 gpm with orange caps, while Class C hydrants provide less than 500 gpm and have red caps. Some hydrants may also be painted violet to indicate a non-potable water supply.

Beyond firefighting, hydrants have several other roles in a community. Contractors may purchase permits to use hydrants for construction projects.

Reduced pressure zone device connected to a fire hydrant at a construction site
Reduced pressure zone device connected to a fire hydrant at a construction site

When doing this, they often use a hydrant meter and a reduced pressure zone device to prevent backflow. Municipal services, such as street sweepers or tank trucks, also use hydrants to fill their tanks. In some cases, hydrants are even used to supply water to riot control vehicles. They can also act as access points for leak detection devices or for monitoring system pressure.

Sometimes, hydrants become part of community life during extreme weather. In 1896, during a severe heatwave in New York City, officials ordered hydrants to be opened to provide relief to the public.

Philadelphia fire hydrant
Philadelphia fire hydrant

Today, some communities provide low-flow sprinkler heads so residents can cool off safely. However, unauthorized use can lead to problems. Vandalism can waste water and reduce the pressure available to firefighters. In many jurisdictions, it is illegal to park near a hydrant. In North America, cars must often stay 15 feet away, a rule frequently marked by red or yellow paint on the curb. If a car blocks a hydrant during an emergency, firefighters are legally permitted to break the windows to run a hose through the vehicle.

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🖼️ Images & Media (7)
File:Downtown Charlottesville fire hydrant.jpg
Downtown Charlottesville fire hydrant.jpg
File:Philadelphia fire hydrant.jpg
Philadelphia fire hydrant.jpg
File:Reduced pressure zone device connected to a fire hydrant at a construction site.jpg
Reduced pressure zone device connected to...
File:Cross-sectional illustration of a typical dry-barrel hydrant.png
Cross-sectional illustration of a typical...
File:Hydrantandcb.jpg
Hydrantandcb.jpg
File:Kawaii fire hydrant cover in Tokyo, Shinbashi.jpg
Kawaii fire hydrant cover in Tokyo, Shinbashi.jpg
File:Dry Fire Hydrant in East Haven, Vermont April 2018.jpg
Dry Fire Hydrant in East Haven, Vermont...
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