I was watching one of the varieties of the Holmes On The Range shows. Mike was literally gushing over the Pex home run manifold that had been installed by his plumber. I gotta admit, it was pretty nice looking. Each curved run of Pex was perfectly spaced, with a long, sweeping, graceful layout. Multiple runs went off to the left and the right, laid out perfectly like a pair of angel's wings. :-)
Anyway, Mike repeated multiple times, each time with more passion, that the system was "pressure balanced", saying that that means "if you are taking a shower upstairs and someone flushes a toilet downstairs, the pressure in the shower won't change."
He wasn't talking about a pressure balanced shower valve or consistent temperatures. He specifically said the "pressure will never change."
OK, so how does that work? If multiple fixtures are opened, doesn't the pressure in the system have to drop? It seems to me that the only way for the pressure to never change as each additional fixture is opened is to have the system running at some specific pressure when only one fixture is open and then have it boosted each time another fixture is opened. After all, you can only have so much pressure in the building to begin with - street pressure - unless you boost it with a holding tank and a pump. There was no mention of anything like that being installed.
What am I missing?