Another fuel tank question replies welcomed

What do you guys generally use for a fuel plumbing system for a standard
non-pumped engine.
I was thinkg along the simple is best line and going for a 2 line system and
just unhook the carb to fill (better than the valve which could go wrong)
With a three line do you have both vents to the top ot one either way. On a
two line well . . you get the idea. could you eleaborate on your present
systems used?
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I always use 3 lines - the 3rd filler line is bent down to lie on the bottom of the tank and I use a simple Dubro black plastic bung filler fitted to the side of the fuselage - it's pretty much obligatory with a cowled engine, and cheaper and less hassle than an in-line valve. It drains the tank fairly effectively, although I do need to tilt the plane forward.
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I have been using the 2 line system for yrs, it is the most trouble free system, and one does'nt have to worry about a disconnect of the less used line,Ray
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I use a two-line system with a Dubro valve. On one plane the valve has been operational for over 7 years and no problems (I know since I just mentioned it next flight it will surely fail :-o). I don't know whether the valve at some point would begin to leak or not but as far as valve failure is concerned it seems that it may fail when you push the spring in to fuel or de-fuel the plane. Your other alternative is not any better either. One could argue that with repeated hooking/ unhooking you may inadvertantly cause a tiny tear in the tube (which would be hard to detect) or cause the tube to stretch and pull out by itself at the wrong time. It is unfortunate that so many of the systems that we use on our planes are single threaded as far is failure is concerned.
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I have used the 2 line system with a fill valve for years with few problems. On some small planes ,I have filled fron the carb end of the hose. To keep it tight on the carb I just cut off a small piece of hose occasionally.
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William Gray
I have used the two line system for ages without difficulty or problems.
I think it boils down to personal choice. Do a good installation job on either a two line, three line, two line system with T and filler valve, whatever - if YOU understand the system and are happy with the operation/idiosnycrasies/whatever, then that is what counts. In my flight box I always carry a hemostat, so even in tight engine compartments I have no trouble grabbing the fuel line from the carb and filling from there with my two line systems, and I always pull the pressure line from the muffler/pipe when doing so. Well, nearly always, sometimes I am real careful as the tank reaches full and carefully stop as fuel starts flowing up the vent line.
Point is, do what is comfortable for you and what you understand or feel to be the most reliable and easy to handle setup for your installation. In the end, what works for you is the best. Not to be esoteric, but really, that is what it is all about. But make sure the tank height, fuel line size, and length of fuel lines are all good in any case and that will take care of most issues.
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MJD has most of the right answer. The only addition I would make is that if you use the 2 line system with a T fitting, there must be a way to prevent fuel from going to the carburetor during fueling operations. With big gasoline engines, the carburetor 'stopper' is provided by the pump if you fill carefully but too much pressure is bad for the diaphragm. I fuel big tanks by gravity, so it is no problem.
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