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• Dry barrel – In areas of the country that regularly experience below-freezing temperatures, the dry-barrel hydrant is most common. As the name implies, when the dry-barrel hydrant is not in use, it has a barrel that automatically drains so it will not freeze and block water flow. The valve seat is at the bottom of the hydrant, which keeps water below the frost line.
The dry-barrel hydrant must be operated in either the fully open or fully closed position. In a partially open position, the automatic barrel drain lets water continuously escape underground at the hydrant base, causing soil erosion and catastrophic damage.
The traffic model of dry-barrel hydrant is designed to shear, or break in half at ground level, in case of vehicle impact. Its design usually lets the base hydrant water valve stay seated on impact, preventing uncontrolled water release.
• Wet barrel – Wet-barrel hydrants have a barrel that is normally filled with water. They are found where temperatures rarely drop below the freezing point. Each hydrant outlet has its own stem and valve seat. Hydrant outlets can be open, closed or throttled in a partially closed position.
Life of a hydrant
Consider the plight of the pressurized fire hydrant, standing idle for long periods, subject to weather and damage from people and cars, but needing to operate correctly and preferably at a high-gpm delivery rate when called upon in a fire emergency.
Damage from unauthorized use, such as by construction workers, street-cleaning trucks or children trying to keep cool in hot weather, can seriously compromise the function of a hydrant. Unique locking hydrant hardware and hydrant operating nuts and caps that can only be operated with special wrenches can solve this problem.
Even authorized non-emergency hydrant use can be damaging to a fire hydrant’s well-being. Following are three real-life examples of “authorized” abuse:
• Broken valve stem – It was almost quitting time at a fire industry trade show, where we were operating an engine from a supply line in a demonstration area. A co-worker shut off the hydrant without notifying me. This hydrant was left-hand, meaning that the stem nut closed the hydrant valve in a counter-clockwise rotation. Intending to close the valve, he ignored the arrow cast into the hydrant’s top indicating the direction of operation. Using the hydrant wrench to force the stem in the wrong direction, he broke it, so the valve was stuck in the open position.
• Water hammer – Several years ago, a fire commissioner from a rural district was fundraising and performing community service by filling swimming pools using the fire department’s 3,000-gallon tanker. He drove the tanker to a neighboring district to use its pressurized hydrant system to top off the tank before making his next stop. He found a hydrant, connected a short length of three-inch hose and filled the apparatus with a direct tank fill. When the tank was full, he slammed the direct-tank-fill butterfly valve closed. Immediately, the fire hydrant “rocketed out of the ground.” He used an axe to cut the hose, and then got out before he and the tanker could be swallowed by the ensuing sinkhole.
• Partially open hydrant – At a northeastern U.S. state fire academy, we were doing new-product development tests on an engine. The academy had the typical dry-barrel hydrants found in geographic locations that experience freezing temperatures. We were accompanied by a new associate who had “lots of fire service experience.” We asked him to connect a short length of 2½-inch hose from a dry-barrel hydrant to the pony suction on the fire pump, and then to open the hydrant valve.
Thirty minutes later, I glanced at the hydrant and noticed water bubbling out of the ground around it. The valve was only partially open, which leaves the integral barrel drain at the hydrant’s base in the open position, undermining the surrounding rock and soil fill, and causing damage.
To ensure that the water-supply system is fit for firefighting, it is essential to have a suitable fire hydrant-maintenance and flow-testing program in your small community, preferably conducted by the water utility.