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A beautiful old vaporstat, but.....

tmw Member Posts: 56
I scored a NOS Honeywell L408B a few months ago. It's over 50 yrs. old in an unopened box.  I tried to hook it up this morning only to find that the thing breaks contact on pressure <span style="text-decoration:underline;">drop</span>.  Is there any way to use this thing on my vapor system that currently runs on a breaks-with-pressure-rise vaporstat?


  • Jamie Hall
    Jamie Hall Member Posts: 17,036
    You could

    rig an SPST relay in there, normally closed.  Power the coil independently through the vaporstat, and run the boiler wiring through the contacts.  Make sure you have enough current rating in the contacts, and check the coil current and voltage ratings too.  Then when the vaporstat is at low pressure, it's open and the relay contacts are closed.  And vice versa...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • tmw
    tmw Member Posts: 56
    OK, got it.

    Thanks. What was the reason that this control was made to operate like this?
  • Steamhead
    Steamhead Member Posts: 14,834
    Some systems with unit heaters

     would use these things to keep the heaters' fans from running unless there was pressure in the system. I prefer to use temperature controllers for this, that way you can run at extremely low pressures as long as the steam has actually gotten that far.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • tmw
    tmw Member Posts: 56

    are you as heartbroken as I am?
This discussion has been closed.