Fire hydrants, also known as fire plugs, connect underground water pipes to hoses on the street. When there is a fire, firefighters remove the caps and attach hoses. Water, under pressure, travels from the pipes, into the hydrant, then into the hose. Hydrants can be above ground (pillar-type) or beneath a lid flush with the surface. In more rural areas, “dry” hydrants allow a fire truck to pump water from a pond or tank.
Types of Hydrants
These are the principal designs of hydrants:
1. Barrel Hydrants
Wet barrel hydrants are always full of water. There is a valve at each outlet, so firefighters can open only the outlet they want. They’re quick and maneuverable because of this. They work great in areas where freezing is not an issue, as there is no water inside the hydrant that can freeze and crack it.
2. Dry Barrel Hydrants
Dry barrel hydrants are for use in freezing conditions. Their main valve is located below the frost line (the point at which the ground never freezes). The structure above ground is kept empty until it opens. Once done using it, a drain valve opens and allows any remaining water to escape, so that it can’t freeze inside the barrel.
3. Flush or Pillar Hydrants
Flush hydrants are mounted underground below a lid at ground level or inside a wall. They are also frequently used in a place where cars or trucks cross over them. There’s a little raised post that pops up from the cover when hoses can attach.
4. Traffic-Resistant Hydrants
These hydrants are designed with a breakaway flange just below the base. If a car strikes the hydrant, the flange snaps cleanly and the top pops off. This limits the ground pipe from bending or breaking. When struck, the top can be swapped out without digging up the entire pipe.
5. Rural or Drafting Hydrants
In areas where city water mains are not available, hydrants may be connected to a large water tank, pond or reservoir or to water taken from a lake or river. These “dry hydrants” are basic pipes that reach down toward water level. A fire engine pumps water in, creating a vacuum that sucks water up into the hose.
Materials and Construction
Hydrants need to be able to withstand high water pressure, rough handling, and weather. Their body is made of cast iron or ductile iron. Internal components, like valves and stems, are made of brass, bronze or stainless steel to resist corrosion. Seals and gaskets are designed with rubber or synthetic materials built to perform.
Most hydrants receive a protective covering, which is typically a colored paint that follows local fire safety color codes. This paint is an easy way to keep hydrants visible and also to protect the metal from rust and from sun damage. Bigger components are the inlet (where the water goes in), the primary valve, the operating nut (to open hose bibb), the barrel, the outlets (the connections of the hose), and the drain on the dry barrel models.
Standards and Regulations
Any hydrant must comply with the rules of safety and water authorities. In the United States, the National Fire Protection Association (N.F.P.A.) issues guidelines for the spacing of hydrants, the minimum volume of water they should deliver, and where they can go. The American Water Works Association (AWWA) standards are followed by water utilities in the manufacture and testing of hydrants.
Hydrant approvals typically are from an organization like Underwriters Laboratories (UL) or Factory Mutual (FM). These tests determine whether a hydrant can withstand high pressure, hold up to corrosion and operate without leaks. Complying with these standards is typically the law, and it plays a role in keeping insurance costs down.
Installation Best Practices
The correct installation ensures a hydrant operates reliably for decades. Key steps include:
- Choosing the Right Spot: Hydrants must be tall, free of things and must not be blocked by parked cars or shrubbery. In cities, they are usually located near building entrances or at street corners, no more than 500 feet apart in areas at high fire risk.
- Burying Below Frost Lines: In colder climates, the leading valve needs to rest beneath the greatest frost line. It prevents the hydrant from being damaged by ground freezing.
- Stable Foundation: A concrete pad or hard, compacted backfill makes it impossible to tip the hydrant out of straight. Pipes can buckle and seals may break if the ground moves.
- Marking and Visibility: Paint that’s visible and reflective markers help firefighters locate hydrants at night or through fog. They feature color-coded tops or collars that index water flow.
- Thread and Connection Types: Outlet threads shall correspond to the local fire hose threads. There are those regions with standardized threads, and there are those who use quick-connect “Storz” fittings.
Maintenance and Inspection
Hydrants are not there for surprise fires. A normal program will usually consist of:
- Flow Testing: Determining the number of gallons per minute (GPM) the hydrant can discharge. Tests also measure water pressure under flowing conditions.
- Opening and Closing: Operating the hydrant fully exercises the valve and ensures smooth operation. Technicians search for leaks and write down any stiff operation.
- Drain Checks: In dry barrel type hydrants, companies check to make sure the barrel is completely drained when closed. If have standing water, dealing with a clogged drain or busted up seat.
- Lubrication: Threads, stems and operating nuts are greased to prevent rust and seizing.
- Cap and Gasket Inspection: Caps should screw on effortlessly and seal properly. Worn gaskets are replaced so dirt or debris won’t make it into the hydrant.
- Winter Preparation: In cold areas, hydrants might be equipped with special caps or heat-trace cables. Any protective cases are inspected for damage.
Selecting the Right Hydrant
Decision-makers compare these when selecting a hydrant model:
- Climate: Dry barrel hydrant in cold climate; Wet barrel type in temperate or warm climate.
- Flow Needs: The number and type of outlets will be based on the flow needed. Standard firefighting requirements may require two 2½-inch outlets, in addition to a larger pumper outlet.
- Pressure Ratings: Municipal or private water systems may have varying pressure. Hydrants are rated to withstand pressure up to 300 psi or more.
- Traffic Exposure: Construction trucks and cars load and unload on the roads, traffic resistant models could be necessary to decrease maintenance cost and potential downtime after an accident.
- Connection Standards: Local fire brigade has different way of couplings. Selecting an hydrant with compatible outlets will facilitate fire fighting efforts.
Conclusion
To keep buildings and neighborhoods safe, it's essential that fire hydrants work well. By knowing the different kinds, how they are made and to what standards they are tested, and how they are installed and maintained, engineers and building and plant managers can select and properly care for hydrants that function well. New materials and devices make hydrants greener and easier to watch. Properly selected and maintained, hydrants can save lives and protect property whenever they are called into service.