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1 pipe steam short cycling (can I get some opinions?)

Norm Harvey
Norm Harvey Member Posts: 684
More info I forgot to mention:

There are no low water issues. the customer does not need to add water enough to indicate a leak.

The boiler water level is relatively stable, though it needs to be skimmed.

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  • Norm Harvey
    Norm Harvey Member Posts: 684

    I went to troubleshoot a 1 ipe steam system that is short cycling. The homeowner had a plumber move around a couple radiators to adapt to some renovations in the home.

    After some initial water hammer problems that were corrected when the plumber cleared some blocked wet ruturns, the customer noticed this short cycling, but he is not sure if the issue existed all the time, or if he is just over sensitive to the operation of his system after the water hammer problems.

    Here's what I found:

    The near boiler piping is as it should be. The newly installed main vents are working properly as the main heats quickly. All the radiators heat all the way across up and down (with the exception of one hot water radiator that has a steam vent up high where the coin vent would be) and the valves do not hiss excessively with the exception of two that will be replaced.

    Once the pressuretrol shuts of the burner, I drop from 1.5 psi to 0.5psi rather quickly, withing 45 seconds. Then the burner fires for about 45 seconds to build back up to 1.5 psi.

    ALL the steam pipes have had the insulation removed, and my recomendation is to insulate the steam pipes and then go from there. The mains should be insulated anyway, so its money well spent.

    My thinking is that the steam is condensing too quickly in the uninsulated mains and risers causing the pressure to drop too quickly.

    My question to my peers is this... Am I missing anything obvious?

    The boiler is fired at the low end of its manufacturer secification, and since the homeowner owns all of Dans books, I'm having him measure each radiator and pipe runs for the EDR since his labor is cheaper than mine.

    So what are your opinions of my troubleshooting methods? Am I missing anything?

    Thanks for your constructive criticsm,
    - Norm

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  • J.C.A._3
    J.C.A._3 Member Posts: 2,981

    Are the main vents properly sized? Could it be that with the new boiler and proper "near boiler" piping...that the main is now filled with steam/temperature, faster than the load can get rid of that amount of air? #1

    #2, Personally, I'd be looking at the radiator vents, and make sure that they are set/adjusted properly,or adjustable, for that matter.

    #3, make sure the pressure control is located properly..AND able to function as designed.

    As I try to TEACH my customers...Balancing steam is not a science, it BECOMES more of an art....once the right lessons are taught by the installer....and LEARNED by the homeowner.

  • Norm, I think you're dead-on

    The boiler is slightly oversized. It can build pressure even with uninsulated mains stealing latent heat from the steam. The bare mains condense steam quickly and that causes the pressure to drop quickly after the boiler shuts down on pressure.

    Once the mains are insulated and you have a good EDR count, fire the boiler to the EDR and watch how well it works.

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  • Brad White
    Brad White Member Posts: 2,398
    I agree with Steamhead

    (Which is not a bad place to find oneself :)

    The mains, once well insulated, will yield immediate benefits. The boiler over-sizing is another issue. As it is now down-fired, I suppose the HO can build an addition? :)
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • fix what's broke first

    Hi Norm,

    I think you have done a great job so far trying to figure this system out and improve it for the HO. With steam it is best to fix what you know is wrong. The boiler cleaning is always the first step in troubleshooting a system, since a dirty boiler (one with oil or impurities on the waterline) can cause many different problems. Any steam carrying pipe needs to be insulated to have peak performance. Take care of these, then proceed to venting.

    Best regards, Pat
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