Wet Barrel Fire Hydrant
Figure 7—Cross section of a wet barrel fire
this design (Figure 7).
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,
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