I have a defunct passive solar system (thanks to the hurricanes of '04), but I hope to restore it soon, perhaps over the winter. I have to do some re-plumbing now, though, and am confused about something.
The return pipe comes out of the filter into a check valve and then to a T connection with a Jandy valve that allows you to send, or not send, the water through the solar panels.
Just downstream (maybe a foot) from the Jandy valve on the line going to the solar panels there's a pretty standard ball valve that does or doesn't allow water to flow along that line.
Why are both of these needed? It seems to me that either would force the water along one path of the other, but plumbing is not my strong point.