Am I on the right track?

Mep4888

I have a three story commercial building that I am working on with Luke warm radiators and very high heating bills. A new boiler was installed about ten years ago, Weil McClain 580, oil fired. Running at about 1 1/2 lbs pressure. It is a 2 pipe system. I have replaced most all the steam traps at the radiators and rebuilt all the f&t traps, open and looked down most of the returns, no blockages and boiler is not accumulating water. When I rebuilt the f&t traps and opened the upstream valve I hear a vacuum breaking and water rushing back to the boiler, so it got me thinking, when they put this new boiler on they cut out the condensate pump assembly, and put the return in higher on the boiler. Is there any chance that they created a water leg and the air cannot escape the system through the thermostatic discs in the f&t traps? If so, should I add a vacuum breaker on the wet return, where and how big? Thanks in advance

Jamie Hall

One is vaguely incllined

to wonder... why are there F&Ts at all?  Is there any good reason why this system couldn't operate solely under gravity?



The radiator traps will -- if they are working -- keep the steam out of the returns, but allow the air into the dry returns -- on which there should be good big vents, by the way -- and the condensate into the dry returns and thence into the wet returns.  The vents (or crossover traps, depending on the system) on the steam mains will let the air out of the steam mains.



So long as when the new boiler was put in some knucklehead didn't lower the water line and convert a wet return into a dry return somewhere -- it has happened! -- the condensate should just happily come back to the boiler without any further help or appliances.



Now if somewhere along the line some of the wet returns were dried out by lowering the boiler water line, you may have a problem -- but there are better ways to solve it than applying odd traps and pumps.  A false water line on the wet returns, to restore the water level in them to where it should be, is the slickest quickest way to go.

Unknown

i concur

What Jamie said... post some pictures and we'll go from there..

Steamhead

What probably happened

was the dry return was venting into the condensate tank, which would have been vented to the atmosphere. When they went back to gravity return, they didn't leave any way for air to leave the dry return.



The vacuum is caused by air not being able to get back in. I ran into this again recently, owner was complaining of uneven heat and hissing valves on the radiators. I found a Vapor system with loose valve packing nuts on the rad shutoffs, and a Hoffman #75 dry return vent that was stuck closed. Any air that got out of there did so thru those loose packings. When I removed the vent it broke a huge vacuum, and I could hear water returning to the boiler. 



Remember, the various traps only route the air from the steam mains and radiators into the dry return. From there, it has to escape somehow. If you were air, could you get out of there?