Two pipe steam problem air locked or steam traps?

Roma

I have a trane two pipe steam system that has in wall trane convector boxes in each room.  My home is a 1936 tudor home approximately 2800 square feet plus an additional 600 square feet in the 3rd floor walk up attic.  I am burning about 275 gallons of oil a month (Yonkers, NY).  This seems excessive to me since the heat is set at 68 during the day (8am to 11pm) and 66 at night.  I recently took off the 2 main vents (hoffman vacuum # 76's) and the two return vents (hoffman vacuum #75's).  I replaced the vacuum vents with brand new Hoffman 75's and and boiled the other two 75 vents in vinegar for an hour and they seem to be blowing fine.  My steam traps were changed about 5 or 6 years ago (i have to check my records).  The boiler is a peerless about 17 years old.  The system also has a large trane bucket trap.  I recently had the asbestos abated as I am redoing the basement.  I replaced all the asbestos with 2inch and 1.5 inch fiberglass pipe wrap.  My problem is my system runs for a good 20 or so minutes but I only get about 5 minutes of heat thru my trane convector boxes.  When I go down to the basement and I check some of the still exposed small fittings they are still super hot but no more heat is coming thru the convectors.  Does this sound like I am air locked or trap problems?  Or any other ideas.  Sometimes the heat cycles on in a half hour other times and hour.  Yet the pipes downstairs are still very help.  How about your two cents.

Roma

vapor stat

I also forgot to add the system has a vaporstat off of a pigtail. the psi is set for about 3/4 of a lb.  and I am at work and do not remember the differential exactly but it is set somewhere near the bottom of the scale. 

Roma

Pressure on the gauge

Also the pressure on the main gauge is showing about 2psi when off but hot and 3 to 3.5 running.  It seems to kick off via the vaporstat when it reaches any more that 3.5lbs.

Jamie Hall

Possibilities...

First thing to check is the real time between when the boiler actually starts to make steam and when it gets into your convectors.  You need to measure the time between when the header at the boiler gets hot and the time when the steam reaches the convector -- that's a much better guide than total running time.



Second, you say that the pipes downstairs are very hot -- steam hot?  A critical question: all of them, or just the steam supply lines?  One of the ways in which a steam system can fail is to have one or more traps allowing steam by into the returns -- at which point the returns may also be steam hot, and the radiators won't be, as they are seeing equal pressure on both the inlet and outlet -- hence no steam flow.  However, if this were the case, the radiator(s) with the bad traps would be nice and hot, and the others cold.  Something to look into.  In any event, the returns should not be hot (warm, maybe, but not steam hot).



3.5 psi is too high -- but I suspect that the real pressure when the vapourstat trips is much more like 1 to 1.5 psi, so it's probably OK.  The 0-30 psi required gauges are none too accurate at low pressures, so the difference between the cold pressure (2 psi) and the trip pressure (3.5 psi) is what you want to look at.  A useful bit of information, though, would be how long does it take the boiler to reach the trip point on the vapourstat?



I have to admit that, depending on insulation, windows, etc. etc. etc., I wouldn't be too sure that your oil usage is excessive.  Sorry about that...

Roma

returns not hot

thanks for the info.  my returns are not hot though but i will triple check them when the heat runs again.  the actual settings on the vaporstat are on the left 2ozs and .01 kg/cm2 (diff) and on the right .02kg/cm2 and .75psi.  The boiler is reading about 3 psi even when it is not running but is still hot.  I looked on a website gwgillplumbingandheating.com (pretty cool) and he talked about steam trap thermographic testing.  anyhow I am a firefighter so i borrowed a thermal imaging camera.  Went home and set the thermostat from 68 to 72 and let it run.  Then I went and checked the heat across the inlet, outlet, and the other side of the trap.  The numbers were all over the place.  Some were on the money 230 inlet, 228 b4 the trap, and 178 after the trap.  Others were 221 in, 213 b4 trap, and 204 after which they are saying would indicate a bad trap.  Anyhow I am having a steam guy come over tonight and look over the system piping and settings from head to toe.