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The Ubiquitous Fire Hydrant

“Form follows function” is a principle typically associated with the appearance of things that serve their purpose effectively without wasted embellishment. Once the function of such an item is determined, its shape then merely shrouds working parts and provides containment.

 

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.

 

Valve Magazine Digital Edition

SPR14 CVR 160x214Inside the Spring 2014 issue…

• Tank Cars
• DBBS & DIBS
• Shale Gas
• New Globe Standard

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