The Ubiquitous Fire Hydrant

This principle is evident in the appearance of the modern fire hydrant. Virtually every aspect of a fire hydrant has a direct part to play in moving water from a buried main to its application on the surface. It’s easy to see why the fire hydrant evolved into a specialized valve resembling a pipe sticking out of the ground.

A Hole in the Ground

In the 17th century, water for fighting fire usually came from a barrel located near a building’s entrance and was thrown by hand onto the fire. This was only effective in putting out the initial flames. In time, pumps were developed that threw water farther and higher, but their effectiveness was still limited by the water source. Water mains, if they existed at all, were made of bored-out logs. To access the water meant digging a pit in the street down to the main. Then a hole was bored into the main allowing water to fill the pit to supply the pumps and the lines of bucket brigades. Once the fire was out, the hole in the main was plugged and the pit filled and marked for future use. This is why fire hydrants are sometimes called “fire plugs”

This method had obvious drawbacks. Precious time was lost finding the main, digging and drilling a hole. Debris from the hole tended to foul the pumps. By the early nineteen century when cast iron began to replace wooden mains, it became common to lay out the cast-iron water system with fire plugs at designated locations. These were cast-iron risers extending from the main to the surface through which the plug, already installed in the main, could be extracted to fill a portable canvas cistern.

Eventually, the plug was replaced by a valve to better control the water, but it was still at the bottom of a riser. Fire crews carried a long standpipe with hose connections they would attach to the valve to bring water to the surface. Once the fire was out, the standpipe was removed and the riser covered, leaving the “fire plug” flush with the ground surface, but little to mark the spot for future use.

From a Hole to a Post

Historic records cite the Philadelphia Water System as the origin of the fire hydrant as we know it in the United States. A post-style hydrant, designed by Philadelphia’s water superintendent in 1803, used a conical main valve made of leather with a brass seat placed on top of the water main. The main valve was connected by a long stem to a handle on top of the hydrant barrel that stood about two feet above the ground surface. Threads under the handle moved the stem and valve up or down when the handle was turned. A separate rod down the outside of the hydrant’s barrel and connected to the handle, also moved to control a small drain opening located below the frost line on the side of the barrel just above the main valve. It opened when the main valve was closed allowing water drainage to prevent freezing in winter. Hydrants of this type are called “dry barrel” because water is only in the upper part of the hydrant above the frost line during use.

One of the more challenging aspects of recording the history of fire hydrant design is the variety of designs that existed, especially from the middle of the 19th century. The variety stems in part from the great pride towns had in their water systems. Hydrants, perhaps the single most visible feature of a system, became objects of that pride and were cast with elaborate surface decorations. Like Philadelphia, almost every water system had its unique hydrant design custom made by a local foundry.

Americans Favor Philly Design

At the time, both European-style “flush hydrants” and Philadelphia-style “post hydrants” were in use. It was also a time when several volunteer fire brigades might arrive at a fire at about the same time, vying for control of the available hydrants. It was pride, once again, that seemed to favor the post style winning out in America. According to an 1865 article, “In the hurly-burly of a fire-alarm...a fireman looks more picturesque seated on the hydrant which he has secured for his ‘machine,’ and can maintain his position better against the next comers, than over a flush case, without such salient points; besides this, it [the post-style hydrant]...certainly looks better in the engraving of his certificate or elaborate art adornments of his engine and fire house.”¹

It wasn’t just exterior decoration that set the early hydrants apart. Several ways were used to control water, including gate and compression main valves, and a “knuckle” arrangement .

Most of today’s hydrants share the basic design concept of the 1803 Philadelphia design. The compression-style valve, now made of rubber, closes in the direction of water flow. Water pressure tends to force the valve into tighter contact with its seat, making it easier to achieve a reliable seal. Modern main valves are made to be removable through the top of the hydrant if repairs are needed.

The stem terminates at the top of modern hydrants with an operating nut instead of a handle. The operating nut is usually in the shape of a pentagon to make it difficult to be engaged by common tools and prevent unauthorized operation of the hydrant. A square shape is also common.

Typically there are two or three threaded nozzles in the top of the hydrant for connecting hoses. The type and specification for the threads can vary; however, National Standard Hose Coupling Thread is now the most common standard used. The larger nozzle, called the pumper, is for connecting the fire pumper truck. It provides the primary supply of water to fight fires. The smaller nozzles are for connecting hoses for street flushing and other utility purposes. For fire fighting, hoses are not normally connected directly to hydrants as water main pressure is insufficient to extinguish most building fires. Until recent years, nozzles were sealed in place on the hydrant barrel with lead packing, making it difficult to replace a damaged nozzle. On newer hydrants, they are threaded in for easier repair in the field.

Color, Color Everywhere

Hydrant paint schemes are unlimited. In some water systems, paint colors show water flow capacity of the individual hydrants. In others the color is chosen to aid visibility of hydrants, or to fit into the local landscape, or even to salute the local sports team.

In modern dry barrel hydrants, an automatic drain valve opens briefly as the main valve opens using main pressure to force flush any debris from the drain channels, and to establish water flow into the surrounding soil, or drain field. Once the hydrant opens fully, the drain closes to prevent water escaping while the hydrant is in operation. When the hydrant is closing, the drain opens again and remains open to allow water drainage from the top of the hydrant. Not all dry barrel hydrants have drains, however, as soil or high ground water conditions may dictate they be plugged or not installed. As part of the annual inspection of such hydrants, a portable pump is used to remove any remaining water before winter.

In warm climates where freezing does not occur, the “wet barrel” design is sometimes used, which is a more compact, simpler design. Typically, each nozzle is fitted with its own valve, which consists of a valve plate with a rubber facing, mounted on the end of a threaded stem. The valve seat is on the back side of the nozzle. Turning the stem moves the valve away from the back of the nozzle to allow water flow. Drain valves are not a part of this design

The fire hydrants found on most city street corners are part of the public water system and are called “AWWA hydrants.” This designation stems from the American Water Works Association, which publishes standards governing the performance and characteristics of hydrants, AWWA/ANSI Standard C502 for dry barrel and AWWA/ANSI Standard C503 for wet barrel hydrants.

Many AWWA hydrants also bear the ULFM mark, which comes from Underwriters Laboratories Inc., a global product compliance testing organization, and Factory Mutual System, a large organization of property insurance companies. ULFM hydrants have met the special requirements of these organizations and are suitable for use in private property fire protection systems.

Basic Design Remains, with Improvements

Modern hydrants include design features not found in the early designs, most intended to make them easier to operate or maintain and to extend their service lives. For instance, oiling systems using food grade oil, grease chambers and plastic thrust washers make the operating nut easier to turn.

Cast iron remains the most common material for fire hydrants, but ductile iron is also used. Water works brass, also referred to as bronze, is used in many of the parts associated with the main valve and drain valve areas, and for the nozzles. O-rings have replaced adjustable packings for longer life and maintenance-free sealing of parts.

Because hydrants are usually located on street curbs and vulnerable to being struck by vehicles, most modern hydrants include a break-away feature. Parts at strategic points, usually just above the ground surface, are designed to fail in a predictable manner when subjected to collision forces. These parts allow the upper part of the hydrant to separate cleanly from the buried portion, and the hydrant to be reset easily.

Contrary to popular belief, this “traffic feature” is not intended to minimize damage to vehicles. The primary purpose is to prevent collision force from being transmitted down the hydrant to its connection at the main, where it could break the connection or cause a leak. Hollywood’s spectacular geyser of water that erupts when a hydrant is hit only happens if a wet barrel hydrant is involved, since the dry barrel hydrant’s breakaway feature and main valve below ground prevent this. Several wet barrel hydrants now have options that prevent the geyser effect.

Specifying and Purchasing

For basic hydrant design parameters, manufacturers look to documents published by the American Water Works Association for municipal hydrants and to the National Fire Protection Association for those used in fire protection systems. Still, state and local agencies have authority to add to these requirements. Manufacturers also incorporate their own proprietary features. The writer of the specification needs to be familiar with what is required in his or her area, as well as what the various manufacturers offer.

In general, the specification might include the specific features required, materials of construction, sizes of various parts such as main valve and nozzles, nozzle threading, size and style of operating and nozzle cap nuts, special coatings, pressure and flow ratings, details of construction relating to making the hydrant easy to operate or maintain, direction of operating and how it is indicated on the hydrant, types of seals and their materials, drain valve arrangement, terms of the warranty, and model designations of hydrants that are typically acceptable.

In addition, when ordering hydrants, certain other details are typically specified, such as the depth of bury (determines how far underground the main valve will be located), color of paint, whether drains are tapped or plugged, number and types of nozzles, size of hydrant (main valve size), size and type of inlet connection, quantity and catalog/model number. Whether or not a specific item is included in the speciation or purchase order can vary.

Installation and Maintenance

Modern hydrants are intended to sit idle for many years, yet must be ready to deliver a large volume of water in an emergency. To maintain this readiness calls for proper installation and periodic maintenance. AWWA’s M-17 Manual for Field Testing, Installation, Operation & Maintenance of Fire Hydrants is used by utilities and manufacturers alike as the guide for installing and maintaining hydrants. In general, hydrants should be inspected at least annually for missing or broken parts, water infiltration through the drains, and signs of main valve leakage. If the hydrant is relubricatable, the oil or grease level should be checked and refilled if necessary. Hydrants should also be operated periodically to assure the mechanism is working without binding.

When installing a hydrant one of the keys to proper operation is to assure the pipes leading to the hydrant are clear of any construction debris, such as rocks that could damage the main valve. Also, because the hydrant is attached to the end of a pipe, it must be set firmly in place on a firm footing and with sufficient blocking or use of joint restraints to prevent movement in use or leakage at its connection to the main. A shutoff valve in the line just ahead of the hydrant is also recommended to allow water pressure to be shut off during maintenance.

The Changing View of Hydrant Security

Fire hydrants must be in open locations and accessible 24/7. This makes water theft and vandalism involving fire hydrants difficult to prevent. Early in the hydrant’s history, theft of water was the chief concern, and they were often covered by lockable wooden enclosures. Later, a pentagon-shaped operating nut replaced the handle as a deterrent.

In recent years as theft of parts to sell for scrap has become more prevalent, hydrant protection devices have become more sophisticated. There are many third-party accessories available to shield the operating nut and nozzles from unauthorized operation or removal of parts. These are “active” devices, meaning they are added to standard hydrants and do not allow access by anyone including emergency crews unless they have the tool that deactivates the shield. Usually, the tool is a special wrench using magnets or uniquely shaped engagement features to access a hidden locking mechanism and allow the operating nut or nozzle caps to be turned.

With the tragic events of 9/11, national and local governments and water utilities are aware vandalism may have more sinister intentions than merely stealing hydrant parts or water. Now there is concern that hydrants represent perhaps the most accessible point for purposeful contamination of the potable water supply, and the commonly used shields may not stop a determined individual.

One of the first devices specifically to address this threat uses an assemblage of heavy stainless-steel bands to wrap the hydrant and prevent turning the operating nut or removing the nozzle caps. It can be locked in place using a hardened stainless-steel barrel lock that the supplier keys and sells only to registered customers.

The active aspect of existing devices and the uncertainty of keeping special tools out of circulation have led to new developments in hydrant security. These new “passive” devices protect the hydrant 24/7 without visible shielding devices. They use a check valve inside the hydrant to block any material from being introduced into the public water supply through the hydrant, on purpose or by accident. Located inside the hydrant, the check valve is invisible and inaccessible, and virtually impossible to overcome. An important benefit of this new approach is emergency and maintenance crews can access protected hydrants as they would an unprotected one.

Currently, there are several products available that use a check valve mechanism. One is an aftermarket device that is retrofit to existing hydrants of any brand. It places a spring-loaded check valve inside the hydrant just below the nozzles.

Another of the devices is offered by a major hydrant manufacturer as an option on its hydrants and incorporates the check valve as an integral part of the hydrant inlet connect. This manufacturer also offers a stand-alone version of the check valve that can be installed on any brand of hydrant that uses a mechanical joint type inlet connection. Because these check valves are located in the hydrant inlet, they do not interfere with normal hydrant operation or maintenance and do not have to be removed. There are also check valves built into hydrant nozzles that can be installed on new or existing hydrants. These, too, do not interfere with hydrant maintenance.

The ubiquitous fire hydrant is recognized by everyone. You can ask anyone what it does and they can give you a reasonable explanation. But ask them how it works and you are likely to get a blank look in return. Perhaps it’s that mysterious aspect of the fire hydrant that makes this protector of life and property so intriguing. Or maybe it’s just its form, not its function, that draws us to it.

Robert Abbott is director of corporate marketing communication for Mueller Co. (www.muellercompany.com). He is a member of the VMA Communications Committee and can be reached at rabbott@muellercompany.com.

REFERENCES

“Papers on Hydraulic Engineering,” by Samuel McElroy, C.E., April 1865 (Vol. XLIX-Third Series-No.4-April, 1865-Page 236) issue of the Journal of The Franklin Institute.
“Development of the Fire Hydrant Parallels Growth of Water Works,” the May/June 1948 issue of Mueller Record.
“Historic Development of the Fire Hydrant,” by L.A. Jackson, September 1944 issue of Journal AWWA.
“The importance of fire hydrant inspection,” by Dick Seevers, Mueller Co. form 11735.