Flexible sprinkler drops are connectors between the rigid piping framework and the sprinkler head in a fire sprinkler system design. The sprinkler head supply line can be either rigidly mounted using a pipe nipple or mounted on what is essentially a relatively flexible stainless steel hose, i.e. a flexible drop, that looks and functions much like the braided metal lines used in faucet installations.
The advantages to the flexible drops are that they are much faster to install, the threaded fitting end reduces the chance of leakage, and since they are furnished in lengths ranging from 28″ to 59″, the sprinkler head can be positioned more precisely over the area to be covered by the sprinkler. They can be used in both wet and dry suppressant systems. Flexible sprinkler drops are used with a bracket that holds the sprinkler head in place. This facilitates positioning the sprinkler head accurately in the center of tiles in a drop ceiling application. Flexible sprinkler drops also provide the adaptability to movement required in earthquake-prone areas.
They must be matched to the supply pipe diameter, which governs total gallons per minute (gpm), so that they do not exceed the ability of the system to deliver equal water pressure to all sprinklers. There are guidelines for the number of bends allowed, governed by the length of the flexible line. The higher initial cost relative to a solid pipe style may be a deterrent to some, but in light of the much lower assembly time, this becomes less of a consideration when pricing out the entire fire sprinkler system. A sprinkler fitter can typically mount 50-60 flexible sprinkler drops in an hour, vs. 6 to 10 of the rigid style.