Negative pressure

rcrit

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?

crash2009

Does it zero

 when you remove it from the pigtail?

nicholas bonham-carter

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

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.

crash2009

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

or just go here....:-)

Link: http://www.heatinghelp.com/forum-thread/132580/Pressure#p1207445

rcrit

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.

jpf321

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)

brian_44

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

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

crash2009

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.............