I've looked at the YS manual and see where they recommend a check valve and a couple filters. However, in addition, I've seen several planes that have externally routed fuel tubing that is sometimes clamped (for some purpose), and a few pictures where shut-off valves have been added. I'm not sure the purpose or use for these devices, nor which of the two (supply and pressure) lines these are added. A little insight would be appreciated.

Larry