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Caleffi Discal not purging air?

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My hydronic baseboard heating system has a Caleffi Discal for air separation (see image below). The overall system operates nicely, at 20 psi, but I am hearing significant air noise from the pipes and pumps. Could it be possible that the Discal is not purging air properly? I don't know if it has been ever cleaned/serviced. Cleaning looks easy (i.e. close valves, open, clean, inspect, put together), but is that something that could cause air purging to stop working and/or do these air separators need regular cleaning?

The Axiom system feeder continues to be completely full (I bought the house two years ago so I have no further history), and I would suspect that if air would get purged, the feeder tank would gradually get emptier. Would that make sense?


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  • hot_rod
    hot_rod Member Posts: 22,505
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    Is the cap on top loose? It needs to be for it to vent properly.

    Super simple to disassemble and clean & check. Isolate both sides, loosen the very top knurled cap to get inside.

    Make sure the hinge is in the proper place to allow the float to move up and down. Check the needle valve in the cap for debris that may have it plugged.

    Can you hear air in the piping at the purger location?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • abackholm
    abackholm Member Posts: 3
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    Thanks for a quick response and the encouragement. I isolated the purger and opened it.

    I want to believe that I found the issue: the float chamber was filled with air, and the bottom of the float had some sticky stuff on it, so I'm guessing it was stuck at the bottom and not allowing the valve to open. Cleaned it, restored the pressure and isolated again - this time the chamber was full of water, clearly different from the first time.

    Restored the operation, fingers crossed that the air will now gradually get purged.
    Alan (California Radiant) Forbes
  • hot_rod
    hot_rod Member Posts: 22,505
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    There will always be about a 1/2” air space on the top. It is designed to keep any floating debris from getting to the needle valve

    You can see that air space in this pic
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • abackholm
    abackholm Member Posts: 3
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    Right - I mean the float was stuck at the bottom and the entire chamber was effectively empty. I am no longer hearing air noises, so I think the clearing was a success.
    hot_rod