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How much derate from 3.5inches down to 1.2 inches

With a standard atmospheric boiler running high fire at 3.5 inches Manifold pressure, what is the input when set at 1.2 inches manifold pressure for low fire. I know its somewhere between 60% and 65% or so, but want an accurate number for some beta testing I am doing on a new steam system concept.
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Comments

  • ratioratio Member Posts: 2,133
    I think the best bet would be to clock the meter, especially if you need more accuracy than 60-65%. I would expect that number to be somewhat appliance-specific, too.
  • ttekushan_3ttekushan_3 Member Posts: 920
    @The Steam Whisperer, I agree with @ratio on that one although knowing ahead of time would be nice. Perhaps engineeringtoolbox has a chart for fluid flow thru orifices at various pressures.

    But now to the giant elephant in this particular room:
    A NEW STEAM HEATING CONCEPT?
    You leave that carrot dangling out there and someone is eventually just going to have to ask. I guess that someone is me today.

    Besides having an edifice complex (big old buildings and all), I’m a sucker for New Steam Heating concepts.

    Enquiring minds want to know...
    terry
  • ch4manch4man Member Posts: 165
    be careful dropping manifold pressure too low, which i believe 1.2" is. most multi stage burners limit low fire to 1.6"-1.7".

    reason being is burner design for proper air aspiration and port loading has its high and low acceptable limits for every individual burner. exceed either and issues such as lifting, blowing, or extinction pop may make your experiment dangerous.

    sounds fun, let us know how it goes
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,103
    Somewhere there are oarfice charts, they used to be in our gas code. I am sure @Tim McElwain would have them
  • Tim McElwainTim McElwain Member Posts: 4,292
    Would first have to know the orifice size and input to the equipment in BTU's. In addition how many orifices are there (how many burners). I have a calculator that can give you that information all the way from pressure at .5 up to 15 inches pressure.

    Example is a 42 drill size which at 3.5" W.C. will give 25,000 BTU's assuming a BTU content of 1050 BTU's per cubic foot. When pressure drops to 1.2" W.C. at 42 drill size input drops to 16,000 BTU's.

    Hope that helps. The tables in NFPA 54 only go down to 3" W.C. The calculator i use is from Bryant and is a catalog # MP-5706. It is called a "Gas Orifice Calculator" on one side and a "Gas Pipe Size Calculator" on the other side.
  • HomerJSmithHomerJSmith Member Posts: 714
    I would expect the methane content per cu/ft is an important consideration.
  • icy78icy78 Member Posts: 274
    > @Tim McElwain said:
    > Would first have to know the orifice size and input to the equipment in BTU's. In addition how many orifices are there (how many burners). I have a calculator that can give you that information all the way from pressure at .5 up to 15 inches pressure.
    >
    > Example is a 42 drill size which at 3.5" W.C. will give 25,000 BTU's assuming a BTU content of 1050 BTU's per cubic foot. When pressure drops to 1.2" W.C. at 42 drill size input drops to 16,000 BTU's.
    >
    > Hope that helps. The tables in NFPA 54 only go down to 3" W.C. The calculator i use is from Bryant and is a catalog # MP-5706. It is called a "Gas Orifice Calculator" on one side and a "Gas Pipe Size Calculator" on the other side.

    Hi Tim, would I be able to get a copy of that MP-5706 by any chance? (Googler didnt produce anything.)
  • Tim McElwainTim McElwain Member Posts: 4,292
    @icy78 I can't seem to find it anywhere on the internet. They were distributed by Bryant Furnace years ago. Check with your local Carrier dealer.
  • Tim McElwainTim McElwain Member Posts: 4,292
  • icy78icy78 Member Posts: 274
    > @Tim McElwain said:
    > (Image)

    Now THATS cool! Thanks for the pic Tim.
  • Tim McElwainTim McElwain Member Posts: 4,292
    There is a pipe size calculator on the other side.
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