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Quick drop in boiler pressure

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Wvega123
Wvega123 Member Posts: 22
in THE MAIN WALL

Hi I have a 100 HP boiler in a NYC co-op building (see pic). I noticed when the boiler stops calling for heat the pressure drops from 2 PSI to zero in less than 2 minutes. Is this unusual?

PXL_20260126_154332886.jpg

Comments

  • ethicalpaul
    ethicalpaul Member Posts: 8,364

    That is expected. When new steam is no longer produced, the steam in the system quickly collapses (condenses) to a small amount of water which greatly reduces any positive pressure to or below zero psig

    NJ Steam Homeowner.
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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,881

    That Power Flame burner has full modulation. If set up correctly the burner should start on a drop in pressure (from the operating control) and go to high fire. As the pressure builds the modulation control should cut the burner back to lo fire or mid fire based on the rising steam pressure. If the burner produces less steam than the load requires the burner will drive to high fire. if THE BURNER PRODUCES MORE STEAM than the system needs it will modulate to low fire. If the building load requires less steam than the boiler produces on low fire the pressure will rise and the boiler will shut down. This lengthens the burner run time and the purpose of the modulation is to balance the burner firing rate to match the load and reduce cycling.

  • mattmia2
    mattmia2 Member Posts: 15,984

    those vaporstats/pressuretorols look conveniently located….

  • Captain Who
    Captain Who Member Posts: 562
    edited January 26
    https://forum.heatinghelp.com/discussion/203583/quick-drop-in-boiler-pressure

    How long have you been familiar with this system? That's about how long it takes with my tiny residential boiler system with a small steam chest partially because I keep the waterline an inch higher then NWL, for, reasons that don't matter right now. My pipes are mostly insulated but there is some missing on a new 16 ft. section of steam main I put in.

    Anyway, the better the insulation of the pipes; both mains and near boiler, and the larger the steam chest, the longer should be this time. Of course, the length and size of the pipes, and the surface area of total radiation (and thus internal volume also) are a factor but haven't changed and probably won't be changed. Is the flue damper the automatic opening and closing type? If it is always open, the boiler steam chest will cool off more quickly. Do you have any idea what was typical for this system?

  • Wvega123
    Wvega123 Member Posts: 22

    Ed, the modulation on the burner only kicks in at 2.5 psi. I set both the pressuretrol and modulation at their minimum so that is what I have. The pressure rarely gets close to the 2.5 PSI. This system was run at 5+ PSI before I arrived. Originally I wanted to use a vaporstat but was told that the power flame doesn't have a modulator at those low levels.

  • mattmia2
    mattmia2 Member Posts: 15,984

    Is the system doing anything that requires higher pressure like lifting condensate to returns above an emitter with steam pressure?

    I don't see why the burner would care where the setpoint is for the high/low transition or the full off transition as long as it didn't result in short cycling. The burner is just putting energy in to the water, it doesn't care if the water is at 2oz/in^2 or 3psig. Unless it is driven by a pot rather than contact closures.

  • Wvega123
    Wvega123 Member Posts: 22

    I'm not worried about the quick drop in pressure just curious. In the rare instance when the pressure cutoff is reached while still calling for heat it will restart again for a short period. That's why I would like the modulation to take place earlier to prevent this. But again doesn't happen often. Yes it has a weighted damper and I do run the water at nowl

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