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Radiator vent won't close and vacuum line vent

I appreciate any help that people can provide. I tried to research this but I could not fix the problem.

I have an issue with radiator vents for a one pipe steam system not closing. The installer for the new boiler that we got two years ago said that the radiator vents were bad and to replace them. New vents or vents boiled in vinegar would soon stop closing properly, so the issue is elsewhere. On this web site I read the idea that if the line vent was too small then the large quantity of air going through the radiator vent would pick up dirt and clog the radiator vents. I want to increase the line vent capacity and see if that will help.

The house is approx. 3000 sq ft and I do not have the line diameters and lengths measured yet. The west line has a Dale No. 5 vent. I plan to remove that and replace it with a Barnes and Jones Big Mouth.

The east line has a Hoffman No. 76 Vacuum Valve. They put the vacuum vent in when it was discovered that the last radiators on the east line had water shooting out the radiator vents. The last radiator on the main floor had water shooting out of the vent like a jet. On the second floor the last radiator on that line had water spitting out the radiator vent. The problem went away when the installer put the Hoffman Vacuum Vent in. My question now is how to increase the vent capacity of the Hoffman No. 76? Should I make an antler and use two No. 76's? Or is there another vacuum vent available that has a greater capacity than the Hoffman? Is there another way to prevent the east line from shooting out water than by using a vacuum vent?

I thank you in advance for any suggestions. It is very annoying on cold days to hear the hissing of the radiator vents. I also worry that with the replacement water needed there will be a large amount of mineral build-up inside the boiler.

Thank you again.


    JUGHNE Member Posts: 11,021
    The first questions will be: what pressure does the boiler run at, has the pigtail been cleaned, do you have a low 0-5 PSI gauge on the pigtail with the pressure control?
  • BobC
    BobC Member Posts: 5,473
    How stable is the water line in the gauge glass when the boiler is making steam? Do you know if the boiler has been skimmed to remove any oils in the water?

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • StephenCzank
    StephenCzank Member Posts: 5
    The Honeywell Pressuretrol L404F 1367 has the Diff at 1.5 psi and the Main at 2.5 psi so the pressure is between 1 to 2.5 psi. The pig tail has never been cleaned. There is no pressure gage on the pig tail. I only have a 0 to 30 psi Internal Syphon gage in another tapping below the tapping for the pig tail.

    The water level in the gage glass bounces up and down quite a bit when the boiler is making steam. The boiler was skimmed four times. The contractor did it the first time and I have done it the next three times. It was amazing the amount of oil that was in the water the first time I did the skimming.

    Thank you for reading my post.
    JUGHNE Member Posts: 11,021
    If the boiler is 2 years old and as you said there was a lot of oil you removed from skimming, your pigtail could have been fouled (especially if iron and not copper/brass) and not giving the pressure control an accurate feel of the pressure. The steam may be having to push thru a partial plug of sludge in the pigtail, requiring higher pressure than needed.

    The controls are seldom accurate with their settings. If you remove the pigtail and clean it, then add a tee/fittings to install a 0-3 PSI gauge under the control. The 0-30 gauge is worthless for our purposes, leave it where it is for code requirements.
    Knowing the operating pressure would be the first step in dealing with the problems you have and many others.
  • Fred
    Fred Member Posts: 8,542
    edited January 2017
    Do you have a Burnham Independence boiler? That Pressuretrol is specifically designed for the Independence boiler (even though I don't know why it wouldn't work on any steam boiler). It is subtractive so it should cu-out at 1 PSI which is fine. The pigtail should be cleaned annually and it would be a good idea to add a 0-3 PSI gauge on there so you can see what is actually going on. If the water in the sight glass bounces more than 1/2" to an inch, you probably should skim it again. How old is the boiler and has any new piping been installed recently? The Dole vent and the Hoffman vent are both small for the mains. I'm not sure why he put a #76 vacuum vent on the one main. They both vent at about the same rate but I believe the #76 is slower to open at the end of a heating cycle. Are you sure it's not a #75? This is a one pipe system, right? (you note radiator vents).
  • Jamie Hall
    Jamie Hall Member Posts: 22,917
    For reference -- the #76 is a vacuum vent. It won't open at the end of a cycle to relieve vacuum; only when the temperature drops.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Fizz
    Fizz Member Posts: 547
    If you're looking for a vacuum vent with more vent rating consider the MEPCO quick vent.
  • StephenCzank
    StephenCzank Member Posts: 5
    Thanks for all the info. I will remove the pig tail and clean it out. I'll get a low pressure gage and use a tee at the top of the pig tail. I saw pictures on this site on how to do it. I will skim the boiler and check out the MEPCO vent.
  • Fred
    Fred Member Posts: 8,542
    There's no reason to put a vacuum vent on that main. Just vent is adequately to evacuate the air in that main.
  • StephenCzank
    StephenCzank Member Posts: 5
    When the new boiler was installed two years ago the last two radiators on the East line were shooting water out the radiator vents. The radiator on the main level had water coming out like a water jet and the radiator on the second floor had water spitting out of the radiator vent. The installer ordered and put in the Hoffman #76 vacuum vent on the east side main and the problem went away. I don't understand what happened but it has worked well since then. I could try replacing it with a regular line vent after I clean out the pig tail and see what happens.
    Thank you for your comment.
  • Abracadabra
    Abracadabra Member Posts: 1,948
    I'm going to take a wild guess and say the near boiler piping is messed up. Do you have a pic of the boiler and the piping around it?
  • Fred
    Fred Member Posts: 8,542
    On a one pipe system there is no reason for a vacuum vent. As said earlier, it isn't hurting anything but he had to have done something else to resolve the problem other than put that vent on there. I am fairly sure the current main vents are also too small to effectively vent all the air out of the mains quickly, Tell us the length and diameter of each main and we can tell you how much and what type vents to put on each main.unless they are very short mains. Clean the pigtail and put a 0-3 PSI gauge on with the Pressuretol. It is also very possible, if the pigtail isn't clogged, that the Pressuretrol is not working or way out of calibration. The new gauge will tell you that. If it's the gray Presssuretrol, it can be re-calibrated but we can deal with that once you can see the actual pressure.
    The fact radiator vents won't close is also one of the symptoms of excessive pressure. They are designed for a max of about 3PSI but that is still to high. Also make sure all supply valves are fully open. Water can't drain if they are partially closed.
  • StephenCzank
    StephenCzank Member Posts: 5
    Well I got the pig tail cleaned out, it was full of debris. The 0 to 3 psi gage is in place and I dialed back the pressuretrol to cut out at 30 oz/sq in and cut in at 5 oz/sq in. Now the vents don't leak except for two which are old and should be replaced. Thanks for the good advice!

    Now for the main vents. I measured the length and the outside diameter and converted the OD to pipe size. At the start, common to both lines are 9 ft @ 4" pipe and 6 ft @ 3" pipe. From there it branches into two lines. The West line has 72 ft @ 2 1/2" pipe. The East line has 62 ft @ 2 1/2" pipe. Currently the West line has a Dole No. 5 and the East line has a Hoffman No. 76 vacuum vent. I appreciate any help in sizing proper vents for the two lines. Thank you again.
  • Fred
    Fred Member Posts: 8,542
    One Barnes and Jones Bigmouth on each end of the mains will be a huge improvement over that Dole and that Hoffman, however, if it where mine, and the vent pipe on each main is 3/4", I would put two Bigmouths on each main.