My pre-existing roof-mount solar panels installation lacks a check valve in the return path. I bought a Jandy 7305, whose documentation states that it should be installed horizontally, or vertically with flow ascending.
Why can I not install it vertically with flow descending? I want the water column above it to drain when the pump is off. As I understand it, the only time the check valve must close is when the pump is running and the diverter valve bypasses the solar panels.