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Vapor steam system...recommendations

Mad Dog
Mad Dog Member Posts: 2,595
what a shame to rip stuff out when you ain't sure of what they is, right? Tank


  • steam problem

    We sold a customer a large Burnham V-9 boiler for a very large residential system. The old boiler had a great deal of radiators and we sold the contractor a boiler feed pump for the job.. This is an old vapor system, no boiler return traps or alternating receivers, simply a vapor system with only a large air vent in the basement. there are no traps or trap like elbows on radiator returns... he replaced all of the radiator inlet valves with Non electric thermostatic valves so it is hard to tell if he had graduated inlet valves on these radiators.... When they started the system up steam ended up in the boiler feed pumps receiver... i investigated and found the ends of the supply mains to be untrapped and simply dumping into return pipe..
    i advised contractor to trap the ends of all the supply mains, but since there are no traps on radiators or on the returns does that mean trapping all the radiators too? Or building a false water line... He simply wants to remove the feed pump and take his chances with a gravity return system. What do you think?

  • I think....

    My first thought is that the old valves were graduated valves, or orificed valves, with each valve sized to only allow enough steam for 3/4 of the radiator's rating to pass. Broomell made one of these, but it had seals on the radiator outlets.

    These were sized to the pressure that the system was designed to run at.

    I think you'll need to install orifices into the union nuts on all of the radiators. It would be easier than repiping to make room for traps on each radiator.

    The question in my mind is how do the mains rid themselves of air?

  • Steamhead
    Steamhead Member Posts: 16,729
    Anything draining into that condensate tank

    MUST have some way of keeping steam from reaching the tank. The radiators either had inlet orifices or water seals in the return-end bushings- if the former, you'd need to add them to the TRVs. The drips from the steam mains would need F&T traps or a false water line- assuming you decide to keep the pump.

    I wonder if that pump is really needed? Remember that when water is boiled into steam it expands 1700 times. If the system is vented properly, the steam expands into it very quickly, and the boiler won't run out of water.

    I would first try bypassing the pump and seeing how the system runs as a purely gravity-return system. Install good-sized vents on the ends of the steam mains and let them drip into a wet return. Also vent the dry return. Then watch the steam fill the system quickly.

    If the pump really is needed, you will need traps or a false water line. These are covered in Lost Art.

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    All Steamed Up, Inc.
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  • and...

    if you decide that the pump is really needed, it is going to be because the water is slow to return to the boiler and the waterline drops too far. This says to me a few things.

    First, to define too far. The waterline, running, reflects the water in the boiler at startup MINUS 1) the water that backs out of the boiler and up the return to define the "A" or "B" dimension. That is usually a couple of "inch and a half" risers that take on up to 28 inches of water from the cold boiler, and 2)the water in the returns that hasn't made it back to the boiler yet, and 3) the thimble full of water that expanded 1700 times to fill the system with steam.

    The normal drop in the waterline from backpressure can be ignored. If you switch off the burner during a cycle, you can see that water come back right away, if the returns are clean.

    In a wide, one story building (think Motel) the returns might be carrying a bit of water. In a house with more than one floor that isn't wide and deep, the returns hold minimal water. You won't need a pump on most of those. Watch out for those loooong motel returns, though.

    The steam consists of almost no water, comparatively.

    SOOoooo, if the returns are clean, the water will come back. If the returns are plugged, the pump won't help.

    Of course, you could put in the tank, pump, and all those traps before you check the returns, which means that after you change the returns, you'll leave the new stuff in for eternity.

    Of course, on some vapor systems, the vent is at the far end of the returns. The pump tank is vented at the boiler end of the returns. It's been my experience that it bangs like crazy on startup if you change the vent location that drasticly. I've seen the air trying to go up the pipe that the water is trying to go down. Water backed up in the mains and hammered until everything got hot and slowed down enough to drain out. Once the air was done getting in the way.

    I can't imagine trying to take an engineered system, and deciding to vent it at the opposite end of the system, add traps and a vented tank, and turning it on.

    But I've seen it.

  • Fred Harwood
    Fred Harwood Member Posts: 261
    Vapor steam

    Is the boiler controlled with a VaporStat? Nothing else will control as well under 1 psi.
  • Right, Fred

    I guess we overlooked the obvious. I assumed that he wouldn't let a vapor system get much above a half pound of steam pressure.

    The 0-16 ounce vaporstat is a Honeywell L408A 1132.

    This will limit the water rising in the "B" dimension, and let that big main vent do the work.

    The higher the steam pressure, the more water you push up the returns. Once the water is high enough to flood the returns, the system won't work right. 1 PSI is equal to 28 inches of water height above the waterline. 2 PSI is 56", and most systems don't have that kind of room.

    Of course, this won't happen with traps and a pump tank. I'm refering to a gravity system, as the contractor was tempted to go back to.

  • To reply to the last question...

    I think I'd make sure the returns are open, install the vaporstat, and run it gravity.

This discussion has been closed.