Multiple Expansion Tanks in a System at Multiple Locations

Tombig_4

I am working on a system in which we are converting a partial steam/partial hydronic system to full hydronic. The existing system had a main steam plant feeding 30+ buildings. In each building there was a steam to hot water converter. Each building was fed hydronically with a circulator, expansion tank, makeup water feed, etc. We are placing several new hydronic boiler plants throughout the development and tying into the existing building systems. The installation was done by leaving the all of the building accessories in place, and trying into the system where the system formally was connected to the converter. The only makeup water feed was valved off. At the main plant, we have circulator pumps, expansion tanks, makeup water feeds, etc. The buildings are two stories, and the main makeup water feed at the plant as well as the expansion tank are set to 12 PSI. My question is, do we need to valve off the expansion tanks in the buildings for a hydronic point of view? For a static pressure standpoint, they are at the same elevation, so they would be set at 12 PSI, same as the tanks in the plant. However, the main circulator is pumping away from the first tank, and eventually towards the second tank. Then there is another pump, the building circulator, pumping away from the second expansion tank. It seems as though the system will be fighting itself from a point of no pressure change standpoint, and the only way to alleviate this would be eliminate the second expansion tank.

I'm getting excessive pressure in the buildings as the main circulators are sized only for the pressure drop in the mains, and the building circulators are sized only for the pressure drop in the buildings, but the first building has a very high pressure on the supply side as it is close to the main plant. Can this be alleviated with a balance valve or some other method?

Any help would be appreciated.

Regards,

Brian