Traditionally, automatic fire sprinkler systems use threaded black steel pipes for water distribution. In the past 30 years, grooved joint fittings (search for "grooved joint fittings" on the Internet) have become a common product for pipes of 2 inches and larger. These connections use grooves rolled into the ends of the pipes and are locked in place by bolted steel collars and sealed by neoprene gaskets. They are as sealed as threaded fittings (or better, if the threaded mold is blunt). Although they are more costly than threaded fittings, they require much less installation time and can therefore provide significant cost savings.

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Connecting the sprinkler main pipe to each sprinkler is a labor-intensive task and requires many threaded connections: screw the pipe joint into the tee on the top of the sprinkler main; a 90-degree elbow; a pipe is long enough to Reach the sprinkler position; another 90; pipe joints of just the right length; coupling; and finally the sprinkler head with a decorative ring (photo 1). If these sprinklers are installed with skill and care, the distance between the deflector on the head of everyone in the room and the ceiling is the same.

In the past few years, pre-assembled flexible fire sprinklers have been developed (photo 2), which are now used more frequently than traditional threaded components. These components are made of brass and stainless steel; have passed UL certification; and have been approved for use by NFPA 13, which is the standard for sprinkler systems. The only threaded fitting screwed into the main tee of the sprinkler (photo 3). Everything else is assembled and pressure tested in the factory, including sprinklers. They consist of a clip on a brass fitting near the sprinkler, which is attached to a crossbar, which is clamped to a ceiling grid or beam, or screwed to a wooden ceiling joist. This is adjustable, so all sprinkler deflectors are at the same distance from the ceiling and have a neat appearance (photo 4). On the right side of the ceiling tiles can be seen the crossbar supporting the sprinklers on the ceiling grid.

The flexible water droplets of the nozzle are made of corrugated stainless steel pipes. Compared with the smooth inner pipes, the friction loss is greater in the water flow process. The friction loss table provided by the flexible water drop manufacturer must be used in the system design to ensure that each nozzle has sufficient water flow during the discharge process.

The flexible water droplets of these sprinklers can be found in new structures with NFPA 13 sprinkler systems; in building additions; and in the renovation of old buildings. The sprinklers are made of black pipes and threaded fittings.

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Gregory Havel is a member of the Burlington Town (WI) Fire Department; a retired deputy director and trainer; and a 35-year fire brigade veteran. He is a Wisconsin-certified second-level fire instructor, second-level fire officer, and fire inspector; a part-time lecturer in the fire protection program at Gateway Technical College; and the safety director of Scherrer Construction Co., Inc.. Javier holds a bachelor's degree from St. Norbert College; has more than 35 years of experience in facility management and building construction; and has taken FDIC courses.

Correction: The penultimate paragraph was updated on February 28, 2018 to reflect some comments forwarded by readers. For more detailed information, please refer to the forthcoming "Letter to the Editor" column in our print magazine.