Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Negative pressure

rcrit
rcrit Member Posts: 74
My newly added 0-3PSI gauge has never really registered much and now it is well below 0 (no bottom pin I suppose).



I checked the pigtail (dicey since I didn't wait long enough for the boiler to cool) and it is clear.



Any ideas?
I'm just a homeowner that has a steam system, take my advice with a few grains of salt.

Comments

  • crash2009
    crash2009 Member Posts: 1,484
    Does it zero

     when you remove it from the pigtail?
  • vacuum in system?

    remember that even though the steam pressures are 1.5 psi or hopefully less, that a vacuum can be negative 14.7 psi.

    if you unscrew the gauge, at the end of steaming, [shut off the boiler], and the pointer returns to 0, then you probably need better main venting. these not only have to let the air out, but also let it back in when the steam collapses and forms a vacuum.--nbc
  • rcrit
    rcrit Member Posts: 74
    return to zero

    Yes, it returned to zero when I removed it from the pigtail and it's at zero now, a few hours after I reset it. Based on the math of pipe size, length etc. my current venting should be more than adequate and the system seems to be balanced ok (finally). Maybe one of my vents is going bad or is otherwise plugged, I'll check that out.
    I'm just a homeowner that has a steam system, take my advice with a few grains of salt.
  • crash2009
    crash2009 Member Posts: 1,484
    vacum

    We were discussing the vacum that is created, between, the water in the pigtail, and the gauge.  It was a few weeks ago, I'll see if I can find it.  I think JPF put a valve on there somehow so he could release the vacum and get zero again.  Check out JPF's November 21, 4:08pm in the following post

    http://www.heatinghelp.com/forum-thread/132580/Pressure
  • jpf321
    jpf321 Member Posts: 1,568
    edited December 2010
    1-pipe Homeowner - Queens, NYC

    NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

    installed: 0-20oz/si gauge | vaporstat | hour-meter | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains

    Connected EDR load: 371 sf venting load: 2.95cfm vent capacity: 4.62cfm
    my NEW system pics | my OLD system pics
  • rcrit
    rcrit Member Posts: 74
    edited December 2010
    vacuum

    jpf, it's interesting that in your picture your 0-3 is reading less than 0 as well :-)



    I'll check out that little valve, I seem to recall seeing something like it at my local big box.



    How does the ptrol do the right thing in the vacuum, or is it between the ptrol and my gauge? If I saw it between 0.5 and 1 lb I'd go away happy, I just want to be sure I can tell that things are working as they should.



    My boiler has been heating pretty well lately so I really don't have a lot to complain about (I haven't seen the bill yet). I'm just trying to get a better understanding of how things are and should be working.
    I'm just a homeowner that has a steam system, take my advice with a few grains of salt.
  • jpf321
    jpf321 Member Posts: 1,568
    it's a...

    1/4" needle valve. I haven't really wrapped my head around what's going on in the pigtail. I don't tend to release the vac much. I also never cycle on pressure. (set at about 12 oz right now due to installed trv's)
    1-pipe Homeowner - Queens, NYC

    NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

    installed: 0-20oz/si gauge | vaporstat | hour-meter | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains

    Connected EDR load: 371 sf venting load: 2.95cfm vent capacity: 4.62cfm
    my NEW system pics | my OLD system pics
  • brian_44
    brian_44 Member Posts: 59
    This may be stupid...

    ...but I popped off the plastic lid and unscrewed the left small screw just enough to stop the needle from going beyond it. It basically serves the same function as the needle stop on the 0-30 gauge. i also noticed when the boiler runs again that needle goes right back to zero, but mine also has a little vacuum in the pigtail- same as yours.
  • steam-rookie
    steam-rookie Member Posts: 128
    I have the same gauge

    When the boiler is steaming it climbs up to 1.4 Oz's

    After the thermostat is satisfied, it starts its way down to zero

    THEN, it goes into negative pressure for about 1 minute

    During this minute of negative pressure the air is being sucked back into the system and I can see the needle slowly heading back to the zero.

    Like I said, after about 1 minute it reads zero. 

    I hope this helps, I also hope that this is normal
    73 year old one pipe system with original American standard boiler, oil fired becket, 2 inch steel pipe main, 100 feet long, with 8 radiators above.
  • crash2009
    crash2009 Member Posts: 1,484
    I have the same gauge also. With 1-pipe gravity.

    and I have a couple conditions that you all may not have, such as a leaking skimmer and sight glass.  And I might have some radiator vents that dont close.  (this place is a long way from tight) My 0-3 gauge goes up to .06 (yes, less than .1) and drops down to zero when the burner shuts off.  My Hoffman 75's clink open about 7 minutes after the gauge zeros.



    I think normal operation (on a tight system) is for the gauge to zero around the same time as the main vents open to allow the cold air in.  If a vacuum  develops and stays there, I agree with NBC that the main vents are not opening.  But hey, the important thing is if you are heating comfortably, who cares?  This kinda statement always riles somebody up.  Just when you think you got it figured.............
This discussion has been closed.