Unidentified device in attic

[Oni Shaw]

I am sure I have seen this device on this board before, but I cannot find the thread. This device was on a plumbing line in the first floor attic area of a 2-story home so it was not at the top of the system. It looks like some kind of pressure relief valve. I could not determine if it was on the hot or cold side or where the tube exiting the top drained to. Electric heat. Home on a well. No steam system in any bathroom. Circulation pump on propane water heater. This device was near the far end of the first floor away from the water heater. (Part of circulation system?)

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[Gregory Booth]

..........I think it's probably a trap primer - are there any floor drains in the vicinity? Maybe a laundry room with a floor drain?.......Greg

[Roy Lewis]

Water Hammer arrester. Maybe!

541-1 - Amtrol 541-1 - 541 Diatrol Shock Suppressor (http://www.supplyhouse.com/Amtrol-541-1-541-Diatrol-Shock-Suppressor?gclid=Cj0KEQiAuJXFBRDirIGnpZLE-N4BEiQAqV0KGgfpZtP3YxDHYOrHspVn7dLfuspR7B767S_Dbt-Q3IAaAiO38P8HAQ)

[Oni Shaw]

Just in case your unwavering curiosity was keeping you awake at night... The winning answer is that it appears to be a float type air vent. The only curve ball is that these normally appear to be installed in conjunction with hydronic systems (not here) or boilers (nope). Reported as "unidentifiable device similar to an air vent - ask seller or qualified plumbing contractor." Moving on to next inspection...