Building Design and Construction Handbook - Merritt - Ventech!

14.54 SECTION FOURTEEN
FIGURE 14.14 Fusible style (left) and glass
bulb style (right) sprinklers. (Reprinted with permission
from Fire Protection Handbook, Copyright
� 1997, National Fire Protection Association,
Quincy, MA 02269.)
14.28 TYPES OF SPRINKLER SYSTEMS
The type of system that should be used depends chiefly on the temperature maintained
in the building, damageability of contents, expected propagation rate of a
fire, and total fire load.
14.28.1 Wet-Pipe Systems
In the United States the wet-pipe sprinkler system is the most common and affordable
sprinkler system available. In consideration of the approximately $1.50/sqft
installation cost, minimal maintenance costs, and the impressive record for reliability,
wet-pipe sprinkler systems should be every engineer’s first choice in sprinkler
protection. The wet-pipe sprinkler system is clearly established as the workhorse
of the fire protection industry.
Unless out of service, wet-pipe sprinkler systems are always water filled. Consequently,
building temperature must be maintained above 40�F to prevent freezing.
Other than a gate valve and an alarm valve or ‘‘shot-gun’’ riser assembly, there are
no devices between the water supply and sprinklers.
To indicate the flow of water as a result of an operating sprinkler or broken
pipe, a local alarm bell on the exterior of the building being protected is required.
For a wet-pipe sprinkler system this alarm feature is accomplished in one of two
ways. In the past it was more common for engineers to specify the installation of
an alarm-check valve in the main supply pipe, i.e. system riser. The alarm-check
valve (Fig. 14.15) is a swing check valve with an interior orifice that admits water
to an alarm line onto which a water-motor-driven gong is attached. To help differentiate
between a water pressure surge and a legitimate water flow, a retard chamber
is often used. The retard chamber acts to delay pressure surges so they subside
prior to causing nuisance alarms. In lieu of a water-motor-gong, and in all cases
on ‘‘slick’’ wet-pipe systems, a vane-type water-flow indicator can be installed and
connected to an electric bell to give notification of water flow. Among the advantages
of using a vane-type water-flow switch are that most models include a variable