steam vents etc.

thfurnitureguy_4

I have just gained access to another apartment on the same side of the building that I have a slow radiator on the floor below. It is the same main and located directly above this radiator It also is not heating. I know I have a main vent problem but I also wonder if where My returns join together is another problem. Lets back track: This building has 2, 3" main pipes that run parallel the length of the building (300')at the celing of the first floor. All of the upper floors are the same with 3 apts. above each side. Basically the same # of rads on each side. The first floor does have 5 more radiators on the left side that are not on the right side. If you time the steam to the main vents in the basement, it takes 5 min. longer to reach the right sides main vent than it takes to reach the main vent on the left. I am assuming that the additional radiators are acting like vents along the main and speeding up the left side. The problem is at the return. There is a very short distance between the left bank and the right bank at the return Y. There is nothing to stop the steam on the faster side,from crossing over to the slow side and closing the vents. I think this is leaving "5 min." worth of air trapped in the slow sides main pipe once the main is closed. The right side is much colder than the left throughout the building. Do I try to time this by subtracting vents from the fast side? or is there a better way to pipe this return? see pict.