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Balancing Vacuum Header

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Does anyone have any ideas or suggestions on balancing the main header for a metro-pipe steam system that works in a vacuum. We have installed riser valves but when the main steam valve is only about 10-15% open some risers don't seem to get the same amount of steam through. All the traps have been checked and/or replaced. The system is pretty tight and can maintain a vacuum. Any information would be appreciated.

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  • Steamhead
    Steamhead Member Posts: 16,832
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    That system is supposed to work

    by varying the level of vacuum rather than restricting the quantity of steam. It would have originally been installed with Dunham Differential Vacuum (later called Vari-Vac) control equipment. Is this equipment still in place and working? 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • MetroSystemAl
    MetroSystemAl Member Posts: 4
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    Varivac System

    yes, we have the dunham bush varivac system in place with a working differential pressure switch. however, it is just that some areas are over or under heted at times...could a defective heat balancer cause this issue? 
  • Steamhead
    Steamhead Member Posts: 16,832
    edited April 2011
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    First thing I'd check

    is whether you are getting the same level of vacuum in all parts of the system. The vacuum in this system extends all the way back to the main control valve rather than being confined to the return lines, though the steam-side is under slightly less vacuum than the return side. You might have to invest in a few vacuum gauges but it would let you see what's really going on. I bet you find some variations corresponding with your under- or over-heating issues.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • MetroSystemAl
    MetroSystemAl Member Posts: 4
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    THANKS!!!

    yes we do have gauges on the return line but only on the main condensate return. that is a great and low cost idea to but a gauge for multiple reutrn lines. thanks forthe advice!!!
  • Steamhead
    Steamhead Member Posts: 16,832
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    Let us know

    how you make out. 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Jamie Hall
    Jamie Hall Member Posts: 23,280
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    I'll add...

    my usual comment about partial port (in this case, partially open) valves and saturated steam -- as saturated steam goes through a partial port and re-expands, a surprising amount of it condenses instead of just expanding.  Which can make for low steam supply (if any!) on the downstream side of a part-open (or reduced port) valve.



    This goes with Steamhead's comment: control your heat on the vacuum side, not the supply side.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • MetroSystemAl
    MetroSystemAl Member Posts: 4
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    Return side control

    yes, agreed my belief was to put valves on the return lines not the supply lines for the simple resaon that the valves might act as a metering device as on a refrigeration system flashing the gas(the steam) causing too much condensation........i will work with what i got and adjust controls through programming to minimize the noise.
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