Hey Marc,
thx for your feedback.
Basically, I agree with you.... although Festo fittings, if used and maintained properly (tubing cut perfectly at 90°) are certified for vacuum operation.
The reason I asked about the fittings is quite simple: When I build a plane, next to trying to achieve an as neat and tidy install as possible, I also try to include some "ease of maintenance". this will help me in not putting off maintanance because it takes too much effort or time. I'll use an example of something I did on the Tomcat. Both pumps, CAT4s and final fuel filters are mounted to a plate that is mounted aft of the cockpit, just in front of the central tank. All connections, both fuel and electrical, are made in such a way that this "module" can be taken out easily. For the fuel lines, this meant having a 6mm Festo connection on the feed line from the tank to the Cat's. rather than having an inline 6/6mm connector, I changed the barbed fitting on the tank caps (A10-style, SM owners will know what I mean) to a 6MM/M5 fitting. one less connection, and I can (more or less) easily unplug the lines from the tank, and more importantly, put them back. If I had kept the barbed fitting, replacing that piece of tube would have meant splitting the fuse again, because there's no way you could get a 6MM line over that fitting, let alone safety wire it... I can even take out the tank caps without having to slpit the fuse....
So, in certain installations, it could be an advantage to have festo's..... just don't use them with Tygon!!!! (as you probably noted I'm no real fan of tygon in jets... ;-) )
Wim