These check valves were included in my Lancair kit and were installed as fuel vent check valves in the fuel tanks in the wings.  They appear to work well, but you need to ensure that the vent lines from the check valve to the fuel tank go downhill toward the tank.  If they don’t, fuel that surges up and closes the check valve, will sit in the line till the valve opens due to suction and then drain out onto the ground and blow back all over the wing tips.  Since we are mixing oil with the fuel it makes quite a mess.

Don’t ask me how I came across this amazing information!  :>(

Bill