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water in steam vent

Hello, contributor FredHarwood2, has mentioned constructing an "inch H2O guage", and the article was about water in steam vents caused by too high steam pressure. I would like to construct one of these, but cannot find the referenced picture on the site or elsewhere. Can anyone email one to me? I fear that my vapostat may be allowing too high a pressure, and want to remedy it. thanks!


  • eugeeuge Member Posts: 4
    The higher the steam pressure in the boiler, the higher the water will be pushed up in the wet return mains that are open to atmospheric pressure.

    I’m not sure about how to go about the h2o inch gauge. But I have another suggestion to get an estimate of where that waterline is without redoing piping.

    I suppose you could stick a Steam pressure gauge on available steam access point above the waterline, perhaps tee’d off the pressure relief port at the top of the boiler? Not sure that’s something advisable for permanent installation, but at least it gives you temporary Independent pressure data. Then using that and the waterline from the sight glass while the boiler is on, you can calculate the height of the water colum in the wet return main.

    You could also get the water pressure reading from a bleed line either at the bottom of the return wet main or another fully submerged valve. Then with that gauge pressure, you should also be able to back out an approximate waterline in the return main, again, while the boiler is on and the system is pressurized.
  • dopey27177dopey27177 Member Posts: 306
    Pressure gauges and water column devices not needed.
    Here is what happens.

    Lets assume the boiler pressure is 1 PSI.
    When the steam travels down the steam main the frictional resistance causes lowers the steam pressure lets say to 7/8 of a pound pressure.

    Te boiler exerts pressure in directions. The one pound pressure in the boiler pushes the boiler water into the wet return.

    Bear in mind there is no resistance to the water flow in the wet return. The 1 psi in the boiler will raise the water in the vertical drop, 2.3 feet in height. The reality is the 7/8 psi in steam main counter balances thee 1 Psi boiler pressure and prevents the boiler water form rising more than 4". 1/8 of a pound pressure
    will raise water 4".

    See dimension A drawings


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