Hydrants are valves made to deliver a large flow of water, hence its name “Hydrant” as it relates to water.
The most common and visible of all hydrants are fire hydrants. Most fire hydrants consist of two pieces, above and below the ground. The head is the part above ground and has the control valve nut and hose ports. The below ground part has the barrel and the valve, as well as the elbow that connects the hydrant to the water main. Two-piece hydrants usually have two 2.5” hose ports and one 4.5” steamer port. The steamer line is the big hose that goes directly into the fire engine’s pumper. The hydrants operate on a failsafe principle, where positive, downward pressure is needed to open the valve. The upper part, or head, of the fire hydrant is connected to the bottom with break-away flanges on the casting and a break-away coupling on the operating rod. This protects both the hydrant and the vehicle from serious damage in case of a collision. Since the valve requires a downward thrust to open, the hydrant will not erupt in a geyser of water if the head is sheared, as it is often depicted in the movies.
Most fire hydrants are dry barrel, which means the hydrant above the valve remains dry when not in use. Not only does this make sense in cold areas to avoid freeze ups, it also reduces corrosion inside and leakage from the hydrant head.
These are similar to fire hydrants and often use the same bottoms and valves, but with a simple one port wide open outlet. They are used to flush out water mains and usually are set up to empty directly into a storm drain or a stream. Water companies will often use fire hydrants for the same work, however specialized hydrants are good for tight, built up areas where the flushed-out water needs to be contained, and to avoid interfering with road traffic.
These are hydrants that come straight out of the ground and are on the top of their feed pipe. Since their outlet and handle are at least three feet above ground, they look like posts. These are usually found on larger grounds such as schools, farms, industrial plants, and building campuses. They have a handle operated valve that you lift up to open with a 180 degree sweep. The cold weather versions will have a long operating stem so that the actual valve is located underground beneath the frost line. They may have a drain so when the flow is shut off, the top of the pipe drains out.
These hydrants are on the sides of buildings, usually leading out of the building’s foundation. They are also called outdoor or garden faucets. These are used by the average consumer to water the lawn, garden or clean cars and windows. They usually have a globe valve that you turn to open, like an indoor faucet, so they can modulate the water flow well. Like the other hydrants, the cold weather versions will have a long operating stem, so that the actual valve is located inside the building. Inside the building, there should be another shut off valve, as well as a drain port so that the hydrant can be completely shut down and drained out for winter.
Fire hydrants are opened with a special five-sided wrench. They should be opened all the way for use, to prevent leakage though its barrel drains, and closed completely, so the upper barrel drains out. The valves are not designed to modulate the flow. External control valves are used for water delivery application where flow control is needed, such as irrigation. Post hydrants have a 180 degree handle that you swing up to open. Their valves are made to modulate the flow of water. Wall hydrants, or outdoor building faucets, are used like a normal faucet with a normal counter clock wise opening configuration.