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End of steam supply connects directly to return?
I live in a house built in the 1920's and its heated via steam. It has main supply lines, a dry return, and a wet return (or used to be a wet return as it sits below the boiler water level). One of the things that I don't understand is why the main supply (seen as the pipe on the right in both pictures attached) directly connects to the return (seen as the pipe on the left) just before going under the concrete without any sort of trap or valve. I find that steam travels down and up the return. Can anyone explain this? Thanks!