Two Pipe return venting problem because of vacum

Steamhead (in transit)

is part of the problem. Since there are traps on the radiators, the steam should be stopped at that point. If steam is getting thru, fix the radiator traps. There is not enough pressure differential between the rad traps and the trap on the return to allow the condensate to flow properly.

The other part is that the water leg in the return is keeping air from venting thru the condensate tank vent. The trap on the return cannot pass air that cannot get to it, and creates a problem for returning water as mentioned above.

You need to add air vents to the return before the water leg, and remove the trap on the return. Use standard main vents such as the Gorton #2. These will open if a vacuum forms in the return.

I wonder if that boiler-feed pump is really needed?



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Rick Hale

I know its a vacum problem... but why?

Having a new boiler installed in an apartment building. System is two pipe system with a return feed pump. Each main has a F&T trap and the return has a large F&T trap (in the boiler room)in the dry return that appears to be working correctly. That trap is needed because of the wet leg in the return on the floor before the boiler feed pump inlet.
The problem is that we are not getting any condensate return to the pump because of a vacum lock in the return. What is wrong... shouldn't the F&T on the return be acting as a vent to prevent a vacum in the return and allowing the condensate to return and be pushed into the pump / boiler. I have read Dan's solution regarding using vacum breaker after the traps at the ends of each main, but why doesn't the large trap on the dry return do this job? Do I still need to install the vacum breakers to get correct return flow? Any advise would be appreciated. THANKS!!!