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  1. #1
    Join Date
    Mar 2008

    Question Air venting valve failure on single pipe system

    We are in our first heating season in a house with a single pipe radiator system (steam). The previous owner had one of the radiators turned off. I replaced the air venting valve on it (it looked like it had been painted over completely) and turned it back on via the supply handle. Sure enough the radiator heated up (a lot of air escaped when I removed the old valve). However, one day later the valve (a Heat-Timer Varivalve) appeared to fail and steam/water escaped from the variable orifice (the spot where you adjust the opening). I replaced it with another Varivalve and two days later more water appeared in a bowl I had set under the radiator. Is there something in this particular radiator that can cause these Varivalves to fail (I have installed at least 7 others without incident in the same house).

  2. #2
    Join Date
    Aug 2007

    Default Re: Air venting valve failure on single pipe system

    The problem rad may have been shut down by the previous owner because it's dirty inside (rust, scale from hard water, etc.) & the dirt bits kept clogging the air vent, so the owner shut it down.

    The air vent has a tiny orifice that closes when the hot steam hits a little alcohol-filled bellows (float) inside the vent---the alcohol expands & a little pin closes the vent so the rad can fill up with steam.

    Any dirt bits can easily clog up the vent---if you can take one of the spare vents apart, you should be able to more easily clean it---otherwise soak it in white vinegar or cleaning fluid, or other solvent.

    The reason the air vent is spitting water & steam is that little dirt bits keep filling it & are not allowing it to close when the steam hits it.

    After cleaning, test it by blowing thru it when it is cold---your breath should pass right through; attach it to a tea kettle's vent on the stove to see if it closes without any spitting when hot.

    This cleaning & checking of the rad air vents also applies to cleaning of the air vent in the main piping in the cellar.

    Make sure the on/off valve (inlet valve) on the rad is ALL THE WAY OPEN so the steam can get in, and the condensate/water can work its way back to the boiler.

    Make sure the water in the sight glass at the boiler is relatively CLEAN-APPEARING; it will never be crystal clear, but if it looks muddy, several gallons should be drained from the boiler drain valve (blown off) until the water clears.

    Another method of clearing the debris from the problem rad is to leave the vent valve off the problem rad for the first part of the heating cycle & allow the steam to blow out the debris (ny times site below).

    This procedure can spurt rusty water & debris into the room, so cover the area directly in front of the vent hole with plastic sheeting or old newspapers.

    You can then temporarily turn off the steam supply at the supply valve of the rad (inlet valve) so you can screw in the air vent without getting burned by live steam.

    Wear heavy gloves on your hands as a precaution, so you don't get burned by the steam.

    This may well clear up the problem if there is nothing else wrong with the rad.

    Also check the pitch of the problem radiator by placing a level (spirit level) along the top of the radiator.

    There should be at least a slight pitch back toward the direction of the on/off valve to allow condensate/water flow back to the boiler.

    When steam enters the radiator, it pushes out the air & heats the rad, the steam then turns to water as it hits the colder cast iron inside the rad & gives up its heat.

    If there is no pitch back toward the pipe, so the condensate water can flow back toward the boiler via the piping, the steam/water will collect in the rad & eventually spit out the vent valve during the heating cycle.

    Also make sure the water level in the sight tube at the boiler is no more than 1/2 way or 3/4 way up the sight glass.

    Also check in the cellar to see if there is a main steam pipe feeding this problem radiator; if there is, the main should also have its own main vent in working order (blowing air out & closing when steam enters the piping.

    A missing or non-working main steam vent will add more debris to the piping & the steam will push it toward the air vent during the heat cycle---continuously clogging the rad air vent.

    If the pitch is wrong on the problem radiator, you can lift the end opposite the inlet valve SLIGHTLY and GENTLY with a crowbar or piece of 2 X 4 & slip a piece of wood, or other material as a shim under the two end feet, so the condensate will flow back to the boiler.

    The heating help site below has a lot of articles on steam heat---click onto "system" when you get to the site, then onto "steam", then onto "Problems with one pipe steam systems".

    Please post back to let us know what happens.
    Last edited by JacktheShack; 03-14-2008 at 06:56 PM.

  3. #3
    Join Date
    Jan 2009

    Default Re: Air venting valve failure on single pipe system

    I have a similar problem. I have a two family house, and each unit has a separate steam heating system. They are both single pipe systems where the water flows back down the entrance pipe as a return. Each system is split into two pipes that feed the left and right side of the house and then come back together with the returning water pipe in the basement. At the end of each line in the basement, after the last radiator, the pipe is running along the ceiling and then drops straight down several feet turns around and runs low to the group with the returning water back to the boilers. About 1 foot after it drops down at the end is where the air vents for the main lines are. I have replaced all of them within the last year, however it seems that they keep getting clogged up with water. The water doesn't spurt out of them or anything like that, but when I remove them to check that they’re working, they are filled with water, so I have to tap them out to get the water out of them. They still work after that if I blow into them they pass the air. Problem is they just fill up again the next time the heat comes on. I assume the returning water is filling the vents as it runs down the pipes and passes over them.

    Is there anything I can do about this, since it seems when they are filled with water they don't allow air to evacuate the line the way they are supposed to?

    Should they be moved somehow to another location on the line?

    Can I add another air vent hole if I want to? Is it as simple as drilling a whole in the pipe? I'm guessing not since it needs to be threaded to accept the air vent. If so maybe I should place straight (180 degree) air vents, not the angled kind, on the top of the pipes since the water will run along the bottom of the pipe and this might keep it clear.

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