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Vacuum return

Viki Ingersoll
Viki Ingersoll Member Posts: 4
in THE MAIN WALL
We have a 1950’s vintage school building with steam. There was a vacuum return system that was disconnected maybe 20 years ago. (Trying to find out if that was when the problems started.) The original pneumatic t-stats were abandoned (?when) and replaced with a single T87 and non-electric radiator valves. Heat is uneven and unpredictable. I’m pretty sure at least one of the non-electrics has failed in the open position. Radiator traps have supposedly been done “in the last few years.” Radiators tend to be warm near the supply, cold near the return. I can hear “glugging” in a return on the first floor, (like the upside down pop bottle) that makes me wonder if condensate is trying to drain but being held back by a vacuum. (We had that at another school w/ non-electrics, it went away when they dropped the pressure from 5 to 2 #.) I haven’t crawled into the 4’ x 5’ tunnel that goes under the school to see what it looks / sounds like in there. Don’t know where end of main traps are or exact service history on them at this point. System was operating at 7 pounds pressure when I was there, water line bouncing 2 – 3 inches, burner cycling every 2 – 3 minutes. I asked the contractor to set the pressure back to 2 pounds, which he did. The school was pretty cool the next morning, so he set it back to 5 pounds in order to get supply to all of the radiators.

I’ve had two different people that I respect offer contradictory opinions on the solution. The guy who sells vacuum pumps says I have to restore the vacuum system to make it work. Another trusted resource says a feed water system instead of vacuum and he’ll come up with some other suggestions if he gets paid to study it in depth. I am also being told that the non-electrics are too large – supposedly sized for the pipe rather than the heating load and that they should be replaced with properly sized units.

Can you tell me in what direction I should start and some of the questions I should be trying to answer in order to figure out how to get this system operating properly?
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