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Vents cycling open and closed - wet steam?

mroberts5 Member Posts: 76
edited January 2019 in Strictly Steam
I am hoping to confirm my understanding of an issue I'm having on four radiators (all connected to the same counter-pitch main).

On all of them:
- the vents are premature closing, then cycling open/closed at anywhere from 2-20 seconds.
- the vent ends are getting hot before the middle
- they're all properly pitched back to the valve (bubble touching line).
- all valves are full open
- I can very clearly hear water flowing out of them.

I know I have wet steam and and planning a repipe to resolve it. My question: Will wet steam cause this issue I'm seeing?



  • Fred
    Fred Member Posts: 8,542
    When you say the "vent ends" are getting hothot before the middle, do you mean the radiator ends are getting hot before the middle? The radiator should get hot from the supply side over to the vent end, one section at a time. It sounds to me like the vents may be placed in the wrong location or they are venting so fast that steam is racing across the radiator and closing the vent. Post a picture.
  • mroberts5
    mroberts5 Member Posts: 76
    edited January 2019
    Yes, the vent end is getting hot before the supply end. And yes, I agree it should be getting hot one section at a time.

    All vents are placed about a third up from the bottom. The vents are either Hoffman 40s or Hoffman 1A set to 1. I've tried Gorton 4, which sort of do the same thing, however they seem to never actually seat (also assuming this is due to water in them).
  • Fred
    Fred Member Posts: 8,542
    Something is allowing steam to move very rapidly across the top or bottom of that radiator to reach the vent. That usually means the venting to too fast. Also, you should not hear water running out of the radiators. Are you 100% sure the valves are fully open (they may seem open but the disc inside the valve may have broken off and condensate can't get out while steam is trying to get in. What pressure is the boiler running at? If the pressure is high, that can also prevent condensate from getting out of the radiator while steam is pushing in. You can't tell actual pressure with the standard 0 - 30 PSI gauge. You need a 0 - 3 or 0 - 5 PSI gauge on the system along with the 0 - 30 PSI gauge (required by code). If the pressure is high enough, I can imagine it pushing water up into the vent and the vent closing on steam and reopening on cooler water.
    A picture is worth 1000 words.
  • mroberts5
    mroberts5 Member Posts: 76
    All four radiators on the same counter flow main do the same thing. Pressure is confirmed at 10 oz max on 3psi gauge.

  • Fred
    Fred Member Posts: 8,542
    It looks good but it certainly doesn't look to have much pitch to the radiator. Do all the radiators in question have the same elbow configuration going into the radiator? That may affect the flow of condensate getting out of the radiator but doesn't explain why the ends get hot before the center sections.
  • coelcanth
    coelcanth Member Posts: 89
    the vent looks like a hoffman 40
    pretty slow vent, no ?
  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    I have several questions for you. 1. When did this problem start? Was it OK in the past? What Changed? 2. Hoffman #40 vents are pretty slow and will work well in most situations. But, Hoffman 1A vents are generally MUCH faster and simply rotating the ring is not reliable. If you remove the screw from the top so that you can see how the rotating ring partially obstructs the vent hole, you will see that even at the slowest setting, if you push the ring from side to side, you will get HUGE variations. I would suggest covering the port about 80%, then see what affect it has. You say some of the radiators are heating at the vent side first. Are these limited to the radiators with 1A vents, or is it happening on #40 vented radiators too.

    How many radiators are in your system? What type? What are the ratings on your boiler? Does your system have main vents on the piping in the basement? What type? Are they working?
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • mroberts5
    mroberts5 Member Posts: 76
    I have two mains, one parallel and one counter flow. Each has a big mouth vent at the end.
    The parallel flow has 5 radiators - these heat fine.
    The counter flow has 4 radiators - these all have the issue described above.

    I am certain this isn't a radiator problem, as all radiators on one main do it, and none on the other do.

    I had my boiler and some near piping replaced in November. I can't say for certain if it did this before, but if it did, I hadn't noticed it.

    I know my near piping is wrong on my counter flow side (no drip - more here: (https://forum.heatinghelp.com/discussion/168043/questions-on-new-gas-boiler), and am thinking this is causing this, but thought someone here might be able to affirm that.

  • gfrbrookline
    gfrbrookline Member Posts: 753
    I am going to go out on a limb and say your pressurtrol is set to run between .5 and 1.5, if not reset it.

    If the above is correct then then vents opening and closing indicates that they are working correctly. As the radiator condenses and cools a bit the pressure will drop and the vent will reopen to breath to let more steam into the radiator. If you read Dan's Lost Art of Steam Heat it is called drop away pressure.

    You do need to figure out why the radiators are not heating correctly though. Are the vents screwed in tightly? What do you have for main venting?
  • mroberts5
    mroberts5 Member Posts: 76
    My Vaporstat is set for 10oz to 4 oz.

    The vents on the counter flow main cycle 10-20 times per pressure cycle. The vents on the parallel flow main cycle with the pressure cycle as they should.

    I have and have read Dan's Lost Art of Steam Heat.

    As stated above, I have Big Mouth vents on each main.
  • mroberts5
    mroberts5 Member Posts: 76
    I just found this old thread https://forum.heatinghelp.com/discussion/143161/how-does-wet-steam-behave

    That sounds similar to what I'm seeing. I'm starting to more firmly believe that wet steam can cause the bottoms and ends to heat up first. Not clear on the physics here...hoping someone can comment specifically on the question of wet steam causing this.
  • neilc
    neilc Member Posts: 2,664
    are all the pipes insulated in the basement?
    known to beat dead horses
  • Fred
    Fred Member Posts: 8,542
    It is very possible, with no drip on that counter flow main and all the condensate having to run back into the boiler riser that the steam is so wet from throwing water around
  • mroberts5
    mroberts5 Member Posts: 76
    > @neilc said:
    > are all the pipes insulated in the basement?

  • mroberts5
    mroberts5 Member Posts: 76
    To follow up: Raising radiator to improve pitch on runout and also raising pitch on radiator helped with this.
  • Jamie Hall
    Jamie Hall Member Posts: 22,901
    Wet steam and your vents on a counter flow main. Yes indeed. The physics is subtle, but consider this: any moisture droplets -- plus condensate -- that get into that main will try to flow back to the boiler, but the steam is trying to flow the other way -- fast. It will tend to carry the water on the bottom of the pipe with it -- which in more extreme cases will cause water hammer. But in less extreme cases, there may be enough -- if the pitch is low -- to cause the steam to be essentially throttled and slow, then the water will be able to flow away, and the steam can come back. If the vents are cycling open and closed in a moderately regular way, I'd consider that as a mechanism.

    The solution is, of course, drier steam or more pitch -- or both.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England