A couple of months ago we repaired a broken dry fire hydrant in Harford County, MD. The hydrant's suction head had been broken off for quite some time. Ownership of the property changed and the FD chose to get the system back in service. The site was an old quarry, so water was clean and plentiful. The problem was determining if the existing pipe could sustain drafting operations....meaning blockages, leaks, etc. With no suction head in place for a few years, the chances of there being "stuff" in the pipe was pretty good. Sure enough, some large pieces of asphalt were found....the product of some vandalism. But, with some good back flushing and troubleshooting, the repair was made and the flow exceeded 1,000 gpm with the new head.
The moral of this story is that before replacing a broken off dry hydrant head, take the time to check the pipe for debris.