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AHA, I think ???

Aha moment with pressure but still???

I have a 100 year old single pipe system in a large Victorian home (9

radiators) that I have been tweaking with many of the recommendations in

3 of Dan's books. Re-insulated lines, new relief valves, balancing etc and have

saved some money and I am now looking at pressure, differential

pressuretrol etc.  The pressuretrol sits on a 1/4" x 8" riser and is set

to cut in at .5lb and out with a 1lb differential, basically it's lowest settings. Great right, wrong I

guess, cuz when I put my shiny new pressure gauge on the same riser and

boiled er up, guess what no pressure. I ordered a 15LB gauge because

that is what was on there and not moving. I can blow about 2lbs pressure

into the gauge manually so pretty sure it's fine and there is visible

steam pressure coming out of the riser but I get no reading.

And so the pressure in ounces ???  Is my system operating on ozs of

pressure? Is it possible that the differential pressuretrol calibrated

in lbs (not ounces) and the 15lb pressure gauge were installed by a

numbskull who should have had a pressuretrol calibrated in ounces?

And??? Do I need a pressuretrol calibrated in ounces or do they even exist?


  • Jamie Hall
    Jamie Hall Member Posts: 15,411
    yes, yes, no

    Your system almost certainly is operating on ounces.  They do, until all the radiation is completely full of steam and condensing as fast as it can.  Then -- and only then -- will the pressure start to rise as the boiler puts out more steam than the radiation can condense.  At which point the pressuretrol -- and yours is fine for a one pipe system -- will cut off the burner until the radiation can catch up.

    Would a vapourstat -- which is calibrated in ounces -- improve things over a presssuretrol in pounds?  Not much, for a one pipe system, and they aren't cheap.  Would a three pound gauge show the very low operating pressure?  Probably... but that's more a matter of satisfying your curiousity than anything else!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • lovesteamheat
    lovesteamheat Member Posts: 4

    Thanks Jamie. The system never gets to the point that the pressuretrol can cut it out. We are having a cold snap and the boiler is working pretty much constantly unless the Tekmar temperature control cuts it out.

    My question still is, given that I now know I'm in ounces: Should I install a vaporstat that will allow low settings or is it likely my system never gets pressured up enough to make that worthwhile?

    It seems if the water is boiling away and all the rads are hot then maybe it could be shut down by the controller for a while.

    Love this wall BTW.
  • Jamie Hall
    Jamie Hall Member Posts: 15,411
    If your boiler

    is happily boiling away and the pressuretrol isn't tripping, then that just indicates that you have enough boiler for your system but no more.  Nothing wrong with that -- in fact, that is pretty much what we all shoot for.

    And, very honestly, I wouldn't spend the money on a vapourstat in your situation.  In a vapour steam system where some of the bits and pieces simply don't work properly on pressures over a few ounces (nothing over 10 on the place I supervise, for instance) one needs a vapourstat to keep the boiler from getting too enthusiastic.  But on one pipe steam, no.  Everything still works up to  pound and a half or so without any trouble, so you don't need it for that -- and in your case, it appears that the sizes are well enough matched that you don't need to worry about it.

    Which is kind of the long 'way around to answer your questions -- first, it is likely that your system never gets up enough pressure to make it worthwhile and, second, that until the thermostat says the you are warm enough in the building, you want the radiation to be putting out all it can, and therefore you need the boiler to keep going to keep steam in the radiation.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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