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Radiator Vents hiss and spit steam near the end of heating

Frankfog2
Frankfog2 Member Posts: 44
edited November 13 in Strictly Steam

A couple of vents on my system tend to hiss near the end of a heat cycle. Especially in the morning after the systems been off all night, but it also happens during the evening when i return from work. i replaced the vents with new maid o mist # 5, but they still hiss and spit. The main vent hasn’t been changed in roughly 20 years, so that could definitely be part of the issue, i’m unsure. The water in the sight glass in about halfway, all the time. Pig tail and gauge are clear and easy to blow though. When the hissing and spitting start, the gauge needle barely lifts, i have a 30 gauge psi, i estimate it’s about 0.5-1 psi when the hissing starts. I’ve also noticed that the pressuretrol often trips shortly after the hissing starts. The pressuretrol will cut off the boiler, and then cut back in, the thermostat will then click off and everything is then quiet.

What are my next steps to isolate the issue? I’m unsure why the pressuretrol is consistently cutting out, there hasn’t been any changes.

Photos Attached

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Comments

  • Waher
    Waher Member Posts: 280

    Your pressure is likely higher than you think. Adding a 0-3psi gauge would tell you.

    What’s your main vent and total length of mains?

  • Jamie Hall
    Jamie Hall Member Posts: 24,713

    Agree with @Waher above. Don't shoot the messenger — the pressuretrol is supposed to cutout when the pressure is higher than wanted. However, it may not be cutting out quite soon enough. Check the level of the pressuretrol. It may be slightly out of level (doesn't take much). It may also have drifted slightly out of calibration; you might try tipping it very slightly to the left.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • AdmiralYoda
    AdmiralYoda Member Posts: 680

    Those 0-30psi gauges are required by code but do next to nothing for us low pressure steam guys. They are notoriously innacurate at the beginning of the range. Install a Tee where the gauge currently is with a couple elbows and put a 0-3psi gauge right beside it.

    Your pressures are probably much higher than you expect. That Pressuretrol you have is a fine unit but not quite the pressure range you want. Yours is 2-15psi. You'll want to be operating at 1.5psi max if you can.

    I'd suspect that main vent is probably undersized or not working too. When I moved in my house the main vents had been removed and capped because they failed. The radiators vents had to do all the hard work getting the air out of the mains. When pressure was highest, typically at the end of the cycle the vents would slam open, vent some high-er pressure air and slam shut.

    New main vents and I never even hear them work anymore. I also switched to a Vaporstat and have a 16oz (1psi) cut in and a 12oz differential. I've saved a lot of fuel and my system is much quieter.

    ethicalpaul
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,309

    Is that a tiled throne upon which that boiler rests?

  • Frankfog2
    Frankfog2 Member Posts: 44
    https://forum.heatinghelp.com/discussion/comment/1819974#Comment_1819974

    yes

  • Frankfog2
    Frankfog2 Member Posts: 44
    https://forum.heatinghelp.com/discussion/comment/1819841#Comment_1819841

    i fear my pressuretrol is damaged because when i try to loosen the diff, the screw loosens. I have it tight just enough to keep it secure. I can’t do lower on the main becausw when i do the boiler cuts out and doesn’t cut back in.

    I’d hate to part with the mercury pressuretrol, but the pressure is slightly higher then i’d prefer. From my understanding there’s no way to fix the diff screw

  • Neild5
    Neild5 Member Posts: 175

    I suspect that the pressutrol is cutting out higher than you think, adding a 0-3 psi gage will tell if that is correct. However, you will need to do more than just add a tee and put it next to the 0-30 gage, it is an internal siphon gage, the 0-3 will need to be protected by a pigtail.

  • Jamie Hall
    Jamie Hall Member Posts: 24,713

    When you say "loosen the diff. screw" what do you mean? Are you trying to increase the differential? Because you should be. The way yours is set in the photograph the differential is set to the absolute minimum.

    Several things to do. First, as has been said, get a 0 to 3 psi gauge and put it on the pitgail with the pressuretrol. Now you will know what is really happening. Next, set the pressuretrol to 2 psig cutout Fire up the boiler. With the boiler firing, watch both the pressuretrol and the gauge. The mercury bulb will start to tip to the left as the pressure rises, and it should tip over at 2 psig. If it tips too soon, very gently tip the whole pressuretrol clockwise a bit and check again. If it tips too late, very gently tip the whole pressuretrol counterclockwise a bit and try again.

    When you get the straight, increase the differential to the point that the mercury bulb tips back to conducting at some resonable gauge pressure…

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England

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