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Vaporstat, how low should I go?

crash2009 Member Posts: 1,484
I was finally at the right time and place to see the vaporstat in action.  It was a pretty cold night here in Ann Arbor (-2 F).  The T-stat was set where it always is (70 F).  I have 2 Gorton 2's  and 1 Hoffman 75 on each of two 75 foot mains.  When I record a cycle I write down the TIME, EVENT, PSI, OZ, and SIGHT GLASS.  also any odd-ball event that may take place.

The V-stat, out of the box was set to 8oz off, and 3oz on.  I am thinking about lowering it a bit to avoid a low water condition.  <strong>I was wondering, if you had recorded this cycle, in the picture, how low would you go?  </strong>

If words can explain a picture here goes.  Everything was moving along pretty normal and events were easy to write down.  When the oz gauge got to 3 and 1/2, things started to change too quickly for me to write down so I just recorded what I could and moved on, trying to keep up with the cycle. 

At 5:54 I think it shut down on low water and v-stat (8oz) at the same time.  I was watching the oz gauge to make sure the v-stat shut the burner at 8, and it did.  Then I was watching the oz gauge drop.  The oz gauge dropped to 3, and the v-stat clicked, then at 5:56 the water feed came on for a few seconds.  Then at 5:58 the burner came on.  The v-stat cycled one more time at 6:01.  At 6:03 the burner went off.  I waited awhile, to 6:19, then went upstairs to check the rads.  They were all hot, even the long 18 and the tall 11.

Knowing that you guys have told me that the vaporstat should shut off the burner, shortly after the last rad is full, <strong>Where should I draw that line?</strong> 

Thanks for reading 


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,216
    You are in the trial and error stage now

    I would not set a customers pressure lower than you have it. The main reason is I do not want to go back for free to turn it up. I am guessing you have a left and right hand screw driver. So drop it an ounce and see. then drop it another ounce. Glad you got it running well.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • crash2009
    crash2009 Member Posts: 1,484
    No mathematical formula huh?

      Yea I have both type of screwdrivers.  Also ambidextrous.  Trial and error it is then.  My griff sense is telling me I want to shut off at 3 or 4 oz.  I guess this is where the frustration begins.  How small of a point spread do these things still work reliably?

  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604
    Thermostat anticipation?

    Crash, do you have a thermostat with adjustable anticipation? If you do, you can adjust it to end the cycle slightly sooner, at the point the rads are completely filled with steam and avoid cycling the vaporstat at all. The thermostat cycle will end before the pressure builds to the cutout setting, and during normal operation you will never reach the pressure limit.
  • crash2009
    crash2009 Member Posts: 1,484
    The thermostat

     is a Honeywell CT87.  The anticipator is set to 1.2 for steam.  Are you suggesting that I knock it down to 1.1 or 1.0?
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604

    If you have it set to 1.2 it is effectively out of the circuit and you have no anticipation at all. I would try gradually reducing the setting until your cycle ends just as pressure builds to a few ounces and the radiators are filled. Then the vaporstat will act as a backup and only cycle on the rare occasions that the thermostat cycle runs longer than usual.

    The mercury T87 is great because the anticipator gives you yet another way to fine tune the system that the newer digital models cannot.
  • crash2009
    crash2009 Member Posts: 1,484
    Hi Ho Hi Ho

    to the hardware store I go.  Need some magnifying glasses.  When I set that anticipator last time I couldn't see the dial.  Thanks, Its nice to be adjusting instead of replacing for a change.  I think I will knock the v-stat down an oz too. 
  • crash2009
    crash2009 Member Posts: 1,484
    Anticipator adjustment

    I adjusted the anticipator tonight.  That dial sure is hard to read.  I set it at 1/2 way between 1.2 and .8 so I guess that means I am set at 1.0

    I am looking forward to recording a 5 am cycle.  Then comparing the cycle to a pre-recorded day, of the same outside temp, to observe the change.  Cycles during the day effect the thermostat too much, with 10 guys opening and closing the front door, showers, cooking, etc. 

    Funny thing about this steam crap, just when you think you know something, you find out you don't know S#$%.
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