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I have inherited a mess of a one-pipe steam system in a 1920’s church. The water use is insane...if that even describes it. The boiler is intact (it passed the flood test with flying colors) so the major leaks only exist in the buried wet returns.
The boiler is a a hopelessly oversized Weil McClain 1180 with a Gordon Piatt gas gun. A model 780 is even a bit oversized based on my EDR calculation of 2135 sq. ft. The NBP is a mess with takeoffs between risers (ugh...). Some bonehead added a receiver tank and two F&T traps at the tank from the old wet returns. When water makes it (rare, due to the insane leakage) these hammer like mad due to a 2 1/2 ft rise in the returns to get to the tank. There is a float valve for makeup in the feed tank that did not have a meter, but now it has a logging meter installed as of last october. See the pictures and cry. The water dept has contacted the church in previous years due to excess consumption! Supposedly some boiler sections were replaced a few years ago (duh...) and the contractor said nothing of the visibly leaking returns or surging/wet steam.
This thing is essentially a one-pass boiler at this point.
The plan is to abandon the wet returns and put in two condensate receivers at the exposed ends of the mains. I believe each main end will need a false water line to bring several drips together before a properly sized F&T trap. I would love to go back to gravity, but replacing the buried lines would require sawing through the slab in a finished part of the basement to excavate/replace the returns. There are low radiators and indirect stacks in the basement ceiling so there is no room for dry returns without creating head bangers.