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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