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Problems with Plastic Fuel Lines
From CP66, Page 3 (January, 1991)
Check that what you order is what you get! Plastic fuel lines must be checked - often.
"Just re-read an article in the Canard Pusher about fuel lines in VariEzes. These "original call-out" Urethane, flexible fuel lines have been reported to deteriorate over time and should be carefully inspected and replaced periodically. Unless the material for these fuel lines is the correct material, deterioration can be very rapid. Visually examining plastic tubing when it arrives from the supplier may not tell the builder/flyer that it is, in fact, the correct material. Even when the correct material is used, deterioration can occur and be invisible to all but an extremely thorough examination. Here is my experience-
Recently, I brought my VariEze home on a trailer and had it in the carport, nose down. It had been sitting there for quite some time awaiting my attention. When I finally got around to it and opened the canopy, I smelled fuel but could find no sign of liquid fuel. Later, I was checking fuel lines under the rear seat by squeezing them with my fingers to determine hardness or brittleness when the header tank fuel line fell off in my hand! This was the source of the fuel smell. With the nose down, fuel had slowly leaked behind the rear seat bulkhead and into the rear cockpit. All of the other fuel lines were discolored to a dark brown but still felt pliable. In removing them from the fitting, to my horror, they easily split and crumbled.
I had always assumed that deterioration would occur in low spots in the fuel lines where water may collect. These failures, however, were up high at the aluminum fittings. They had been installed in July of 1983 and flown for a total of 750 hours, so they were seven year old. I have used auto fuel, regular, when at home and IOOLL Avgas when traveling. Lately, regular auto fuel is no longer available locally so I have been using auto unleaded (no alcohol). I have, on occasions, used Marvel Mystery oil as a fuel additive and, many years ago, I used TCP.
I believe that VariEze fuel lines should be changed at least every three years and great care should be taken to orde@ the correct material. Also, make sure you receive the correct material. As a further safeguard, cut a few small pieces of the new fuel line and submerge some in a bottle of gasoline and some in a bottle of acetone. I check these samples from time to time for any obvious signs of deterioration.
Editors comment: Thanks for your report, Byron. We agree wholeheartedly with the suggestion to change plastic fuel lines at least every three years. Also, we have found that buying polyurethane-type tubing from a supplier like McMaster Carr (locations in Chicago, Los Angeles and New Brunswick, NJ) will get you a receipt that spells out part numbers. For example, according to McMaster Carr's catalog, Tygon tubing comes in at least two material types, one called out for fuel and lubricants, another for food and beverage! Each material has its own part number. Tygothane, the material originally called out in the VariEze plans, is recommended for fuels and lubricants. Using McMaster Carr, at least you have the verification of the part number on the receipt. We highly recommend this company as a source of an unbelievable variety of materials, tools, etc. Their catalog is an awesome tome!