Subject: Dry pendent head failures in walk in coolers

I have been receiving an increasing number of reports of dry heads failing in walk in coolers in supermarkets and large volume discounters. (Cosco, Albertson’s etc.)  It appears that the majority of the problems involve Central/Star/Gem heads, (why are those names so familiar?) I contacted Tyco Technical Services at (800-381-9312,) and Kerry Bell of U.L.  After a lengthy conversation with Tyco, I finally got a reasonable response.

It seems that when Tyco quit manufacturing heads with o-rings, and began using only Belleville seals, there was no longer an o-ring seal at the top of the tube. This lack of an upper seal apparently allows the passage of air to enter the tube from both the weep hole on the bottom and the un-sealed top. As one would suspect, this allows condensation to build up more quickly, then freezes building up ice, until "parts break".
Tyco Technical Services did not believe it made a big difference whether the head was glass bulb or link type, or where the head was located in the freezer. The two dry model sprinkler heads manufactured by Tyco that have been experiencing the most problems are the Models S-170 and F-960. When I asked Tech Services if other manufacturers had experienced the same problem as Tyco, they responded that apparently some manufacturers had fewer problems than others.

Tyco has re-designed the upper inlet and now manufactures the Model DS-1 that has an upper seal, (hopefully not an o-ring.) A technical advisory from Tyco on the issue will be issued shortly. However, one must still be very careful, as apparently Model S-170 and F-960 are still being installed.  Kerry Bell informed me that in the not to distant future all dry heads will have to pass a U.L. condensation test, and all sprinkler heads will have to pass a U.L. "corrosion test".