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Understanding Steam Boiler Start Up Logic

Guyser69
Guyser69 Member Posts: 2
in Strictly Steam

Sorry if this is a simple question, or if it has been asked before. I understand the purpose of a Pressurtrol is to stop firing the boiler when the pressure climbs to the cut out setting and then to restart firing the boiler when the pressure drops to the cut in setting. When a boiler hasn't been running for a while, and the boiler pressure is zero, what by passes the Pressurtrol to allow the boiler to start firing to get to operating pressure?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 25,214

    You kind of answered that yourself. The pressuretrol (or vapourstat) is on, allowing the boiler to fire, at any pressure less than the cutin pressure — so when the boiler is cold and the gauge pressure is zero, the control is on and the boiler will fire (all other safeties OK).

    As the pressure rises eventually, in most systems, it will reach the set cutout pressure, at which point the control opens and the boiler stops firing. As the pressure drops, it will reach the cutin pressure (you set the amount of drop with the differential) and the control closes again and off you go.

    No bypass is necessary — the control is aways on below the cutin pressure.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ethicalpaul
  • LRCCBJ
    LRCCBJ Member Posts: 678

    Think of the Pressuretrol as a disconnect device. It's normally closed and only opens (the electrical circuit to the control) when the pressure rises above the setpoint. Then it opens and the boiler stops until the pressure falls and the Pressuretrol closes again.

    Ideally, the Pressuretrol never opens…………..if the system is designed properly and the boiler is the proper size for the radiation.

  • Guyser69
    Guyser69 Member Posts: 2

    Sorry, I've been thinking about this for three days and it wasn't until I posted the above question that I figured out the obvious answer.

  • LRCCBJ
    LRCCBJ Member Posts: 678

    It's nice when we get a very simple question that requires a instant answer to fix. 😁

    Usually it goes the other way with steam systems.🤢

  • Jamie Hall
    Jamie Hall Member Posts: 25,214
    https://forum.heatinghelp.com/discussion/comment/1825849#Comment_1825849

    Don't feel bad. You're not the first to be slightly confused by this!

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England

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