Construction Concerns: Dry

Hydrants deserve more attention than we give them. Gregory Havel takes a closer look at the components of dry-barrel hydrants.

Article and photos by Gregory Havel

Hydrants deserve more attention than we give them. Hydrants are built to comply with American Water Works Association (www.awwa.org), American National Standards Institute (www.ansi.org), and National Fire Protection Association (www.nfpa.org) standards, and are tested for compliance with these standards by Underwriters Laboratories or Factory Mutual.

Photo 1 shows a dry-barrel hydrant that is completely assembled and connected to its water supply pipe, positioned in its trench, and stabilized by a nylon choker from a backhoe excavator so that it can be braced, blocked, and backfilled. The short piece of gray plastic pipe at the top of the black hydrant barrel holds the tracer wire that is installed with every water main and hydrant water supply so that the location of the pipe can be determined accurately in the future.

Photo 1. Click to enlarge

Looking at a dry-barrel hydrant from top to bottom, we can see:

Photo 2. Click to enlarge

Photo 2 shows a detail of the underside of the break-away flange at the base of the dry-barrel hydrant. The bolts pass through the hydrant’s base flange and the two-piece safety flange, but not through the flange on the top of the buried section of the hydrant barrel. This allows the two-piece bottom flange to break if the hydrant is struck by traffic without damaging the rest of the hydrant. These flange bolts can be loosened to rotate the top of the hydrant as needed.

Photo 3 shows the valve seat flange and the 90° bend at the bottom of the hydrant that connects to the water supply. The small round hole in the rectangular opening in the valve seat flange is the dry-barrel drain port. These hydrants are designed so that this drain port is open when the hydrant valve is closed. When the valve is only partly open, the drain port is open, discharging water into the ground, loosening the soil. This can cause hydrant failure.

Photo 3. Click to enlarge