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If anybody could help I would appreciate it.
My 750 is nearly complete at as a kit. When I built the wings I ran the supply fuel lines at the lower fitting and the vent line to the fuel tank on the opposite side on top of the tank. At the time I didn’t consider what type of engine I was going to install. Now that I have decided to install a fuel injected engine, I realize that I need use the vent lines I ran for the return of the fuel to the tanks. But because there are only two fittings in each of the fuel tanks I don’t know how I am going to be able to vent the tanks at this point. I’m going to be using an “Andair” duplex fuel selector valve to return the fuel from the same tank that it was taken from. What I would like to know is there any way at this point to vent the tanks without disassembling the wings and if not, where do I install the vent lines?
I’m sure by now you realized this is my first build. I would greatly appreciate any suggestions. Thanks in advance, Bob
Comment
I have the Zenith vented caps and mine don't vent. Check them carefully because some of the caps were pressed to tight and don't vent.
I agree with Andrzej that a header tank or venting to the main tanks is required. If you check the Sky Tek Canada design for the 912is they put a lot of effort into venting, using 1/2 inch lines between the header tank and the wing tanks nand venting the vapour return line into the header tank. I have to disagree with Doug's suggestion of venting to the gascolator because if you vent there there is no place for the vapour to escape and it will remain in the line feeding the engine causing fuel starvation due to vapour lock.
Bob, standard Zenith fuel caps are vented. The additional fuel fittings at the outboard top of the fuel tanks are optional vent/return ports. On the 750 I built we didn't even use the extra port and filled it with an aluminum pipe plug. In fact, the additional port was only on the left side tank as the tanks we used were some of the first to come with the new fittings.
One other place you might consider returning your excess fuel too is the top of the gascolator. I'm not sure if the Zenith gascolator has the extra port on top but the basic homebuilder's gascolator from Aircraft Spruce does. With the gascolator ideally being upstream of your fuel pumps, it will back feed to the tanks without having to run a complete set of return lines to the tanks.
Another thing to consider when running fuel lines is the material the lines are made of. I personally will not use the black rubber automotive grade fuel line Zenith sells for their kits. You are building an airplane, use aircraft grade fuel lines and fittings (ie: 3/8" aluminum line and AN fittings). The additional costs involved in installing a proper aircraft grade fuel system are well worth the piece of mind. I have experienced the black rubber fuel hose swelling internally and cutting off fuel flow on a classic car I have so figure it is an accident waiting to happen if rubber fuel lines are used on an aircraft. Maybe I'm just picky but the electrical and fuel systems on both of the planes I have built have adhered as close as possible to standard aircraft methodology. These standard systems have been developed as the result of accidents caused by systems that did not work as intended. Yes, genuine aircraft components are more expensive but you know they will work as intended.
Hope this info is of some help. Best of luck with your build.
Doug M
NW Ontario, Canada
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