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Low pressure system at higher pressures?

David Tetreau
David Tetreau Member Posts: 15
in THE MAIN WALL
What a surprise to find the boilers serving a low pressure system that are actually rated to produce 15psig steam, but the controls are set to operate at about "3 to 4 psi" according to the maintenance people. Most days it hovers near 5 psi that I have witnessed. I have always heard bad things about operating boilers at any other pressure than design.

Also, this system's terminal equipment is designed to work on 2 psi, with a vacuum return at 3" Hg.

The owner now wants us to install a PRV, operate the boilers at 15psi, and set the PRV to 2 psi that serves the connected load at the original system design pressure.

There are over 100 radiators, two small air handlers (6000cfm & 2500 cfm), and a snow melt system running off these boilers.

Any comments on what is going on here (other than lying) and how we can reasonably run this system?

Comments

  • jeff_51
    jeff_51 Member Posts: 545
    well

    the speedometer on my tahoe goes to 130 mph, don't mean I go that fast. Usually the lower you can run your steam system the better, but of course with a commercial system that was designed to run at a certain system pressure, thats what you need to do. Was this system designed, or cobbled together and added on here and there?
  • Bob_19
    Bob_19 Member Posts: 94
    15psig

    and lower is considered to be lo-pressure, 16psig and over is considered to be hi-pressure.
    A boiler is designed for either lo-pressure or hi-pressure.
    All lo-pressure boilers are designed for 15psig max, but hi-pressure boilers are designed for various pressures as needed up to thousands of lbs.

    They may not be generating enough steam at lower pressures to carry the loads.

    The problem with running a lo-pressure boiler at 15psig is that the safety valve is going to leak in short time. Running so close to lift is not good for the valve. The building engineer should know this.
    This brings up another problem, people without a clear understanding of the importance of the safety valve will try to defeat the valve somehow when it begins to leak.
  • EBEBRATT-Ed_4
    EBEBRATT-Ed_4 Member Posts: 6


    There is a certain percentage of the safety valve set point that you are not supposed to run up against to ensure that they won't weep. I think a 15 psi safety valve the high limit is supposed to be set at a max of 12 1/2 to 13 psi. Can't remember the percentage. An ASME rule I beleive
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