Actually, this is not always true. Many HX loops have restrictors that significantly restrict the flow when pulling a shot. In this case, almost all the flow comes through the non-restricted tube.Nunas wrote: Incidentally, when one brews with an HX, the water is drawn via both the top and the bottom tube and the circulation effect stops.
But it is true that the circulation stops. On my KvdW, the flow in lower tube actually reverses direction.