Down-Feed two Pipe Steam system

Joewasey

I am Working on a down-feed two pipe system in an 40 unit apt building. Some of the down-feed piping is not heating up. The rads all have a Trane B-1 trap or they were replaced with a 17-C trap. Also at the bottom of the feed is a B-1 or (17-c replacement). A number of the feeds are not heating up, mostly replacements. Alot of work was done over the years by people guessing, such as return lines not being pitched and working down-feed risers were tied into none working risers with 1" copper. The attic piping is not accessible, Should main line vents be on this two pipe system? Also on the none working drops/risers the 4th & 3rd floor rads work, not 2nd & 1st. Does anyone have any info on these systems.

nicholas bonham-carter

There may be a diagram in the library/museum here for either a Dunham or Trane down feed system. It is just like an up feed system in its need to get the air out. Any old system like this needs low pressures to work properly (under a pound, verified by a low pressure gauge). A search here for down feed, Trane or Dunham should help you find details of a some proprietary air removal device, which maybe designed to keep the air out for sub atmospheric operation. There are often some check valves in the returns for this, and they may have frozen shut.
There must be some sort of crossover traps at the very end of each return which are not working properly. The upper floors work because the higher pressure enables the air in the riser to be compressed down to the second floor level by overpressure.
When you discover the weak link in the first riser which is the culprit, I am guessing, the others will be found to have the same problem.
an IR camera might help find bad traps which are letting steam into the returns and closing other traps from the return side.--NBC

Jamie Hall

Where do those traps at the bottoms of the down feed risers go? They were probably intended to cross over into a fuly vented dry return or returns. It would be worth checking those traps (do they work???) and the lines into which they feed (are they vented? Pitched to drain?)