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Maid O Mist model 1 question

I just bought a pair of the maid o mist model 1 vents and both of them have the removable vent cap with a "D" stamped in them. Now, am I supposed to just remove the cap and leave it open to be a properly size #1, or is this just a mixup at the factory or something?

Checking the specs on the maid o mist vents, model 1 is definitely supposed to be bigger than model D.


  • ethicalpaul
    ethicalpaul Member Posts: 5,702
    edited January 2022
    to my recollection, Gorton and Maid o' Mist #1 are functionally equivalent to #D of each make.

    They both use #1 to indicate a main vent with the 1/2" and 3/4" threads and #D to be a radiator vent with the 1/8" threads. So it's probably less of a mixup and more of "We're out of ones stamped #1 so let's use these ones stamped #D since they are the same"

    What rates were you seeing for them I'm curious?

    But in the end, you can remove the orifice at the top of the vent and then it will be as large as any MoM vent can possibly be. Sizes #1 and #D is basically the same as "no orifice at all"
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • KC_Jones
    KC_Jones Member Posts: 5,737
    A 'D' radiator vent vents the same as a #1 main vent. Could be they just use the same cap for both.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Kruthers
    Kruthers Member Posts: 10
    Uh jeez, you guys are right. I somehow misread the spec sheet and thought the 1 and D were different. Must have looked at C instead... Anyway, thanks for the sanity check.

    As for rates, no idea, just a homeowner. But the annoying thing is that the end of the main where I put the #1 is still cold when the radiators in the thermostat room (which I just put MOM #4s on) were completely hot.
  • NYtimebomb
    NYtimebomb Member Posts: 30
    Things to try on your cold main:
    Take off the vent on the main that is cold and see if steam gets that far.
    Close the valves in front of the hot radiators, then see if the main gets hot.
    Hold a flame near the main vent #1 outlet at the start of a cycle to see if any air is being forced out (may take a few minutes).
  • Kruthers
    Kruthers Member Posts: 10
    Thanks for the suggestions. I do know air is coming out of the new main vent though, I can hear it and stop it with my finger. It's just seems weaker than I expected. But I just now got the 2nd main vent replaced after some struggles, so I'm going to monitor things for a few days.

    I'm pretty sure both of the old main vents were completely blocked so I'm hoping to see SOME improvements.
  • Kruthers
    Kruthers Member Posts: 10
    So it looks like the vent I was complaining about is just defective. The 2nd one I installed (same size vent on the other main) vents much more air than the first one did, and now the first one has petered out and stopped entirely.

    So just gotta get a replacement, again.