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Does higher pressure lead to more leaks in our single-pipe system?

cubicacres Member Posts: 358
We noticed after reviewing several months of our boiler log notebook that we use much more water (even after adjusting per boiler hour of run time each day) on the colder days. We suspect the longer cycles reach higher pressure we can sometimes observe on our 0-3psi gauge we added to our 2 pressuretrolls, pushing water out of some areas at 1.50-2.00 psi that didn't leak much at lower 1.2, 1.0, 0.7 psi, etc. pressures.

Does this seem likely? If we added a vaporstat to have more accurate control over pressure, could we top out at 1.3-1.5 psi to get 1.0 psi at the farthest radiator 50-100 feet away from the boiler on the 2nd floor at the other end of the building? Would this stop many of our leaks & save energy on shorter burner run times as well?


  • Jamie Hall
    Jamie Hall Member Posts: 22,100
    Well, I wouldn't guarantee any particular amount of leak reduction from a pressure change, but...

    Since the flow through a leak is more or less proportional to the pressure (actually the square root of the pressure difference, but let's not get picky), it does stand to reason...

    On top of that, though, is that some types of leak -- such as valve packings, but any leak with a little flex in it, won't leak at all at lower pressures, but will at higher ones.

    Running at a lower pressure is almost always a good thing. I doubt that you need even 1 psi in the far reaches of the system (consider: vapour systems usually run at around a tenth of a psi at the boiler!).

    Now... would it result in shorter run times? Probably not. That's much more a function of how much heat you need in the structure. Would it stop the leaks, again -- probably not, but it would lessen the amount of water lost.

    One might be inclined to wonder... can you actually find and repair the leaks? That would be well worth the effort.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • dopey27177
    dopey27177 Member Posts: 887
    Typical one pipe steam systems below 1500 feet above sea level operate just fine at a maximum of 1 1/2 psig at the boiler.

    Your vapor stat or pressure controller should be set at 12" (3/4lb) to 1 1/2 psig.

    As to your water loss check all your radiator valves, if they are loose or wobbly or to easy to turn you will need to tighten the packing gland or repack the valve. These valves can leak so little that the water dries up before hitting the floor.

  • Steamhead
    Steamhead Member Posts: 16,454
    Good to hear from you, @cubicacres !

    I'll second the packing nuts on the rad valves, unless we already went over that when I was there several year ago. Also the rad vents, as these will wear out over time. How's the system running otherwise?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    JUGHNE Member Posts: 10,898
    The school I am working on now had a 4" flange leaking to where it had a bucket hanging under the drip. It is in a tight corner with immovable pipes connected to it.

    When the pressure was running at 5-7 PSI (upon bad advice from large company "pro") it leaked quite steady.
    The pressure was set down to the lowest possible on the pressurtrol...2.25 PSI.
    The bucket has been dry ever since.
  • gerry gill
    gerry gill Member Posts: 3,076
    I personally don’t believe one needs “pressure “ to heat with. You need about one ounce of pressure per hundred feet of pipe. How many hundred feet of pipe do you have? My experience has been that every system that doesn’t have some peculiar reason to run higher pressure (air handler coil, f&t lift etc) works better with a vapor stat and leaks less from air vents.
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

    JUGHNE Member Posts: 10,898
    Pressure drop is based on pipe friction and the number of fittings, if I understand correctly.

    Now, can you have pipe that is too large??

    I am revising a system and will have an existing single pipe main that starts at 5" and is 4" for the remainder.

    A 2" main would carry the connected load.

    I am pretty confident it will work but look at the sizes and wonder will the steam get "lost" in such a large pipe.......crazy huh??
  • Jamie Hall
    Jamie Hall Member Posts: 22,100
    No, it won't, @JUGHNE -- though it will move slower. But not that much slower. The same volume will get to the radiators -- and it actually won't fill that much slower, either, assuming you've insulated it, since the apparent velocity from the boiler to the main vents is much more dependent on heating up the main than it is on how fast the steam will move once it's hot.

    Don't hit your head on low hanging pipes, though!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 10,898
    Thanks Jamie, this had worked before with a max of 2.25 PSI, so I should assume it will work at less than 2 PSI.
    I am separating a single pipe system from a 2 pipe system ( 2 buildings that had zone valves).

    Other than some minor AC work this is my summer vocation/mission, I spend too much time in the boiler room and think too much. Also have drawn the NBP out numerous times over the last 2 years.

    The pipes will eventually get insulation.

    I am blessed with 10 foot high ceilings, however I did add a 4" header between the twin boilers just at nose level, but there are lower pipes to keep you from walking between the boilers.

    Have long rags tied to them for now as a warning....watch your head!
    Eventually FG insulation will cushion the blow.
  • cubicacres
    cubicacres Member Posts: 358
    Thanks everyone! We'll check the radiator valves & air vents again. Many valves on the floor are/were very old-maybe original from 1900 since some were wood & we replaced about 1/3 of the 20-25 radiator valves in the building the last few years. We also used graphite strings to re-pack the valve stem nuts on several more. Seems like this is a never-ending process to hunt down those leaks :s

    I was under the impression 1lb psi at the far radiator was a good target to aim for. With 100 ft of pipe to the far radiator on the 2nd floor of the 5-unit building, 1-2oz psi drop should be all that usually occurs. Then with a vaporstat rather than our less precise presuretrolls & our 0-3psi gauge we have a better chance of fine-tuning it to 12oz cut-in to 18oz cut-out pressure or even something several oz psi less than that range?

    If I'm thinking about the steam movement correctly, it will still push out to the radiators enough to heat the rooms per the thermostat requirements even if the pressure causes a cut-out that stops the burners? This leads to the fuel savings, but still allows the steam to push out to the radiators since there's still a (smaller) pressure differential at each radiator air vent? Is this using the momentum of the steam produced & being "patient" to let the steam find its way to the radiators rather than keep running the boiler too long & having that extra several oz of pressure build-up in the system?