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The sprinkler family tree
09/10/10
Supplying water to sprinklers from more than one path has been used for generations.
There are three basic layouts for sprinkler systems. The original systems were
designed in a “tree” layout that supplied water through a cross
main, which acts like the trunk of a tree. (See Figure 2, page 46.) Sprinklers
are located on branch lines attached to the cross main, and the arrangement
resembles a tree.
The second layout is the “simple loop” system, where a second cross
main is added. (See Figure 3, page 46.) The extra cross main splits the water
supply into two paths to a flowing sprinkler. The increased hydraulic efficiency
allows the use of smaller-diameter cross mains and branch lines.
The third layout is used to increase hydraulic efficiency even more. It's the
gridded layout, where additional cross mains are used to form the grid pattern.
(See Figure 4.) All of the pipe sections are interconnected, so water flows
through each. The specific path depends on the location of the flowing sprinkler.
Compared to a simple loop system, the multiple paths compound the number of
loops, and thus the name compound loop system.
The H-inch multipurpose system is a form of a gridded system. (See Figure 5.)
The only difference is that the multipurpose system uses flexible nonmetallic
pipe that attaches to the multiport fitting at angles. Thus the pipe sections
travel in arcs instead of right angles like rigid pipe.
Unlike tree or simple loop systems, water flows through every pipe section
and sprinkler fitting in a multipurpose system each time a plumbing fixture
is opened. This offers two technical advantages:
1. The volume of water flowing in each pipe section is relatively small and
has a corresponding low velocity. This allows the system to supply the required
volume of water to sprinklers with a lower supply pressure.
2. The sprinkler system is constantly tested. Every time someone opens a plumbing
fixture, water flows through the entire system. If the plumbing is working,
so is the sprinkler system
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