Fire hydrants, also known as a standpipes, are located along various points on a water mains network. A hydrant standpipe allows the flow of water from the main to feed an attached firefighter’s hose to put out a fire.
Above-ground fire hydrants got their start in the 1800s, but underground hydrants were in operation in Asia and Europe as far back as the 1700s.
Fire hydrants may be referred to by other common names, such as “fire plug” or “Johnny pump” depending on the locality. In the old days, before fire hydrants were invented, firefighters had no choice but to use bucket brigades or hand pumps to deliver water for putting out fires.
Nowadays, firefighters connect their fire hose to the hydrant and opens a valve to release water from the water main to the hose. Hydrants can be fitted with various kinds of valves so that they can be connected to a desired to water source, either pressurized or not.
Most fire hydrants are designed to accommodate a rate of flow of no less that 250 gallons (about 950 liters) per minute.
There are generally two kinds of hydrants: the dry barrel and the wet barrel. The wet barrel hydrant contains a constant supply of water, while a valve needs to be released to let water flow.
The principal advantage of a dry barrel hydrant is that it avoids the situation where the water supply can get frozen in cold weather. Some wet barrel hydrants are made of bronze in place of iron, or they may be given a rust-resistive coating on the inside.
The barrel of a fire hydrant is what gives its “standpipe” name. Some hydrants may be rounded, while others be more angular.
The outlets are usually made of bronze to ward off corrosion in this vital part that connects to firefighter hoses, but the caps may be of other metal.
Hydrant standpipes are generally manufactured to work with both key and bar or ball valves. They may be available in fixed or swivel heads, and equipped with single or dual-head discharge couplings.
The double or dual-headed standpipes are attached to a common base section, but can be installed as a single head by inserting a blank plug into one of the outlets.
In cases where the standpipe will be tapping a drinking water main, then the practice is to insert a one-way or no-return check valve to prevent contamination of the main water from unsafe water that can flow back from the hose into water system.
While the primary purpose of hydrant standpipes is to supply water for fire or other emergency situations, the local water utility may allow licensed uses. fire hose nozzle