A fire hydrant is a pipe that allows water to flow from a water main with the control of a valve in order to put out a fire. Above-ground fire hydrants originated in the 1800s, but the underground type was used in Asia and Europe as far back as the 1700s. In the United States, a hydrant may also be called a "fire plug" or a "Johnny pump," depending on the region.
Before the invention of the fire hydrant, firefighters used the bucket brigade or hand pumping systems, of getting water to put out fires. A hole had to be dug in order to retrieve water from the water main and firefighters would pass buckets of water from the hole along a line of firefighters to help get water to the fire. Since the newly dug holes had to be plugged up after the fire call, the term "fire plugs" began to be used.
A firefighter connects a fire hose to the hydrant and releases a valve to get water from the water main. The different valves on a fire hydrant allow it to be attached to different water sources that may be either pressurized or not pressurized. Most hydrants are designed to allow not less than 250 gallons (950 liters) of water to flow through the hydrant per minute.
Many different patents were used to create various fire hydrants. Wooden outer encasements were used before the more familiar cast iron cover commonly seen today. The American Water Works Association (AWWA) regulates the design of hydrants in the United States to meet fire district standards.
Dry barrel and wet barrel are the two kinds of fire hydrants. The wet barrel type holds a constant water supply, while the dry barrel type needs to have a valve release to let water in. The main benefit of a dry barrel hydrant is that its design avoids a frozen water supply in very cold climates. Some wet barreled hydrants may be made of bronze rather than iron, or they may have an inside finish that avoids rusting.
The barrel of a fire hydrant may also be known as a "standpipe." Some are rounded in style, while others have more angular lines. The outlets on a hydrant are usually made of bronze, but the caps may be made from other types of metal.