Construction Concerns: Sprinkler Head Flex Drops

Fire sprinkler head

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By Gregory Havel

Traditionally, automatic fire sprinkler systems have used threaded black steel pipe for water distribution. In the last 30 years, groove-jointed pipe fittings (search the Internet for “groove joint pipe fittings”) have become common for two-inch pipe 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 seal as well as threaded fittings (or better, if the threading dies were dull). Although they cost more than threaded fittings, they require so much less time to install that there is a significant cost savings.

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Connecting the sprinkler mains with the individual sprinkler heads was labor-intensive, and required many threaded connections: a pipe nipple screwed into the Tee on top of the sprinkler main; a 90-degree elbow; a piece of pipe long enough to get to the location of the sprinkler head; another 90; a pipe nipple of exactly the right length; a coupling; and, finally, the sprinkler head with its trim ring (photo 1). If these sprinkler drops were installed with skill and care, the deflector on every head in the room would be the same distance from the ceiling.

Pre-assembled flexible fire sprinkler drops

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In the last few years, pre-assembled flexible fire sprinkler drops have been developed (photo 2), and are now more frequently used than the traditional threaded assemblies. These assemblies are made of brass and stainless steel; are UL-listed; and are approved for use by NFPA 13, the standard for automatic fire sprinkler systems. The only threaded fitting screws into the Tee on the sprinkler main (photo 3). Everything else is factory assembled and pressure-tested, including the sprinkler head. They include a clip on the brass fitting near the sprinkler head that attaches to a cross-bar that clips to the suspended ceiling grid or bar joist, or is screwed to wood ceiling joists. This is adjustable, so that all the sprinkler deflectors will be the same distance from the ceiling, for a neat appearance (photo 4). The crossbar that supports the sprinkler head on the suspended ceiling grid is visible at the right side of the ceiling tile.

Attachement to sprinkler main

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Final appearence of sprinkler head through drop ceiling

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The sprinkler head flex drop is made of corrugated stainless-steel tubing, which has greater friction loss during water flow than pipe with a smooth interior. The friction loss tables provided by the flex drop manufacturer must be used in the design of the system to ensure that there will be adequate water flow to each sprinkler head during discharge.

These sprinkler head flex drops can be found in new construction with NFPA 13 automatic sprinkler systems; in building additions; and in remodeled sections of older buildings whose sprinkler head drops were made of black pipe and threaded fittings.

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Greg HavelGregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 35-year veteran of the fire service. He is a Wisconsin-certified fire instructor II, fire officer II, and fire inspector; an adjunct instructor in fire service programs at Gateway Technical College; and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 35 years of experience in facilities management and building construction; and has presented classes at FDIC.

 

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CORRECTION: The penultimate paragraph was updated on February 28, 2018, to reflect some observations forwarded by a reader. See an upcoming “Letters to the Editor” column in our print magazine for further details.

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