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Venting capacities with pressuretrol vs. vaporstat.

shawn_11 Member Posts: 24
This site is addictive, Thanks to all giving the good advice.

Under Hot Tech Tips, Balancing one-pipe steam systems, the advice for lowering the pressure in a system states: “If you set the "cut-in" setting at one-half psi on a pressuretrol, or at about four ounces on a vaporstat, you'll never lock the air vents closed.”

Why would one-half psi (seemingly 8oz) on a pressuretrol be equal to 4oz on a vaporstat?

And more importantly, how do I reconcile the one-half psi on my pressuretrol (as low as it goes) to Gerry Gill and Steve Pajek’s venting capacities chart (“Balancing Steam Systems using a venting capacity chart”), which deals with pressures from 1-3 oz?


  • gerry gill
    gerry gill Member Posts: 3,078
    the pressuretrol

    is acting as a high limit point..but the most venting takes place as steam starts to leave the boiler when the pipes just have atmospheric pressure in them..so the most venting is taking place before pressure is biulding up..picture the boiler starting, then steam builds, it starts pushing air, first at vapor, then at 1 ounce, then at 2 ounces, then at 3 ounces..see how that works..at these low pressures is when the vents matter..one would assume the vents to be closed by the time you've achieved the pressuretrol setting..hope that helped.

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  • shawn_11
    shawn_11 Member Posts: 24

    thank you, that is helpful. The current vents are so small that steam almost never makes it all the way down the radiator to close off the vents. (the vents are well below what would be recommended from your charts.) i assume that is one factor that has kept my bills high in the past.
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