Wing Fuel Sumps

[6896]

My choice of drain valve is the SAF AIR CAV-170 with a 7/16-20 thread and MS29513-012 O-ring. The hex on the valve is recessed into the wing a bit (inside the sheet metal), but the push-in portion of the valve extends outside of the sheet metal. I don't have my notebook handy, but I recall that the hex portion of the valve was recessed into the wing inside the lower sheet metal by about 9/16 in, which is why I had to machine extensions that had one end in the form of a male 7/16-20 end with O-ring, and the other end a 7/16-20 female end boss fitting for the CAV-170 to screw into. Parker Fitting makes such an adaptor that we modified a bit by drilling out and re-facing the female seat to shorten it up a bit. I looked around for other drain valves that might stick our farther, but all of them had hexes that were recessed inside the wing.

[6896]

Here are the photos that I referenced in my prior post to show that the bottoms of my left and right fuel cells are equivalent and neither is "pushed in" to change depth of where the fuel drain valve sits with respect to the lower wing skin (inside or outside).