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Mysterious vacuum in one pipe system

nicholas bonham-carter
nicholas bonham-carter Member Posts: 8,576
edited January 2022 in THE MAIN WALL
At the end of a long burn, when the temperature has dropped, and finally the thermostat is satisfied, and has cut off the burner, I get a sudden drop of the waterline in the sight glass-low enough occasionally to trip the reset on the probe LWCO! No doubt this is due to a vacuum developing in the supplies somewhere. The water slowly returns in 10 minutes, I have washed out the Gorton 2’s, (3X5 mains), but it is hard to determine the temperature of their reopening.
This usually happens at night, and I still suspect the gas company of juicing up the mix of gas, so as to have over-fired the boiler, and made sure the entire system is full of steam. Maybe they are compensating for their new dinky little plastic hoses, installed 2 years ago, along our street.
Can I use check valves installed at the end of my venting antlers, (6), as vacuum breakers?
How many feet of 2 inch pipe can be filled with 6 gallons of water?
A check valve like this 3/4 inch Nibco?—NBC


  • Jamie Hall
    Jamie Hall Member Posts: 22,934
    A swing check, like that one you show, is nowhere near sensitive enough to either open when you want -- or close against steam.

    If your boiler is properly piped (pictures might help) creating a vacuum in the steam mains or radiators cannot pull water out of the boiler. If it is a two pipe system, however, creating a vacuum in the dry returns only can, however, so the first vents to check are those on the dry return -- if you have a two pipe system. On the other hand, if you have a two pipe system the vents on the dry returns should never close in the first place...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,021
    I have read here that some with 2 main vents on an antler noticed that the smaller one, say G1 would open and let air in before the larger G2.

    Perhaps because of smaller body cooling down quicker.

    I have tried the true vacuum breaker, it takes too much vacuum to actually open it even when adjusted way down.
    EBEBRATT-Ed Member Posts: 15,335
    That check valve will work fine . You can put it on the boiler if you like. 35' of 2" pipe holds 6 gallons of water
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Thank you. I have 6 returns dropping down from the mains, next to the boiler, with 3 Gorton 2’s on each.
    That means 5-6 feet could be siphoned up into each one, until the Gortons open up.
    The odd thing about this is its newness, starting late last winter, just after the new gas main in the street. Shortly, the gas company will drill in a new feed for us from the street, and the old 3 inch iron pipe will be abandoned. An ugly bank of 7 wireless readout meters will be in front of our noses as we come into the kitchen.—NBC