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Leaking Shutoff Valve

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Nick11
Nick11 Member Posts: 11
edited March 2022 in Strictly Steam
My shutoff valve is leaking steam, not water, at the connection of the cap and the body. (not from the packing nut).

See attached picture and arrow pointing at the joint.

I've try tightening it, putting teflon tape on the threads and still the same.

Asking for advise on what sealant would help best in this case without replacing the valve.

Want to try to see if I can fix it without hiring someone for the job. Last time I had a valve replaced, ended up replacing the radiator too.

Also curious if the cap, top part are interchangeable. I could buy a new valve and put the new cap on.

Thanks,


Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,303
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    The seal at that joint is not on the threads, but on the flat surfaces between the bonnet (the removable part) and the body. Ideally this should seal without any sealant of any kind -- but the surfaces can get scratched, or the bonnet overtightened and warped, or...

    So. The best bet is to take the bonnet off completely (turn off the boiler first!!!!). Then take a look at those sealing surfaces. They must be really clean -- no old sealant, corrosion, scratches (if possible). You can clean them with fine sandpaper if need be (but be sure to go evenly. If in doubt as to whether you can do that, wrap the sandpaper around a rigid sanding block). Be sure and check the sealing surface around the edge of the bonnet, too. Then you can form a gasket with a VERY thin bead of RTV sealant (auto parts store). Then screw the bonnet back on. Make sure it isn't cross threaded! And go easy on the gorilla bit Ten foot-pounds torque will be ample, and use a wrench that fits -- not a pipe wrench.

    If by cap -- top part -- you mean the bonnet, the above procedure should do the trick, unless the old one is cracked or otherwise damaged.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Nick11
  • Nick11
    Nick11 Member Posts: 11
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    Thanks Jamie,

    Was focused on the threads. Nice to know how the valve actually works.

    Didn't know overtighten would be an issue in this case.

    Will check the bonnet, but based on your info, a new one wont create a new problem assuming that the rest of the valve is working properly.

    Asked about replacing just the cap/bonnet cause wasnt sure if the threading inside was made to pair.

    Thanks again.
  • JUGHNE
    JUGHNE Member Posts: 11,061
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    If your system is running pressure above 2 PSI, lowering the pressure has cured a few leaks, if you're lucky.

    If not then the parts from the exact same valve of brand name and size might fix it.
    It has to be an identical twin.
  • Nick11
    Nick11 Member Posts: 11
    edited March 2022
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    JUGHNE said:

    If your system is running pressure above 2 PSI, lowering the pressure has cured a few leaks, if you're lucky.

    Digging through the website, looks like I might have a faulty pressuretrol. It is set at 1. But shuts off when the gauge, on the same pigtail, reads closer to 3.

    Will try repairing at the bonnet / valve part, to see if it works.

    This heating season is coming to an end. Getting a new pressuretrol for the next season.

    Thanks.
  • mattmia2
    mattmia2 Member Posts: 9,653
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    Is the gauge a low pressure gauge like 1-3 psig or 1-5 psig? The code required gauge won't be accurate at steam pressures.
  • Nick11
    Nick11 Member Posts: 11
    edited March 2022
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    mattmia2 said:

    Is the gauge a low pressure gauge like 1-3 psig or 1-5 psig? The code required gauge won't be accurate at steam pressures.

    It is a 1-15 PSI one. Is that still too broad?

    Comparing it to the larger one thats attached to the body of the boiler, it is usually about 0.5 PSI less in reading.

    Should I get a lower one, the 1-5 PSI one?

    Do you have a recomended one? Not to much work if I replace it the same time when I put in a new pressuretrol. They are connected to the same pigtail.
  • JUGHNE
    JUGHNE Member Posts: 11,061
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    Are you sure the pigtail is clean?
  • Nick11
    Nick11 Member Posts: 11
    edited March 2022
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    JUGHNE said:

    Are you sure the pigtail is clean?

    Pretty sure. Put in a new brass pig tail 4 years ago and been cleaning it before the start of every heat season. Last time was Oct 2021.
    JUGHNE
  • mattmia2
    mattmia2 Member Posts: 9,653
    edited March 2022
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    JUGHNE said:

    Are you sure the pigtail is clean?

    They said they are on the same pigtail, so even if it is clogged, the pressuretrol and the gauge are seeing the same pressure.

    Although I suppose if it is restricted there could be a case where the pressure builds faster in the boiler than at the control, it overshoots, then the pressure at the gauge and pressuretrol catches up.