[TAKPAK]

Just went through another class where propane valves and tanks were a "hot" topic. Per the manufacturer, the "center" position is nothing. It does not shut off both tanks, nor does it draw from both tanks in that position. It's just "there" to cause us to ponder things, I guess. Manufacturer wouldn't say any more, due to liability concerns, most likely (we might take the valve apart to see???). Otherwise, what John Kohl says is correct about the "left/right" positioning of the selector switch, the red/green indicator, etc.

I personally have a 40 pound tank on one side, and the standard 30 pound on the other. The 40 is my "main" tank, the 30 is a backup. Also, a 40 pound wouldn't fit on the one side, due to positioning of piping.