I've been thinking about this idea of not having a mechanical fuel pump on a VW aircraft engine. There are several planes that dispense with it in favor of the electric pump because the pump in the stock position can cause a bump on the cowling. This seems dubious from a reliability standpoint, which is why so many people have multiple electric fuel pumps, backup power supplies, etc.
But an idea occurred to me. I had to replace a fuel pump 30 years or so ago on my VW Beetle, and the pump is operated by a bump on the camshaft. As the camshaft rotates, a pushrod is moved up and down by that bump and the top of that rod operates the pump. This means there's no need for the stock pump to be located ON TOP of the engine. It could be anywhere around the case that would let the pushrod reach the camshaft. The pump mounts on a moveable plastic block (and there may be a bore inside the case to guide the pushrod -- I don't remember -- but it would be fairly easy to cut this out of a junk case). In this way, you could mount a stock VW pump to one side, allowing a normal cowling and reliable fuel pumping with just one backup electric pump. When I had to replace my fuel pump, my car had gone more than 100,000 miles. Mike Taglieri On Aug 17, 2016 1:35 PM, "Jeff Scott via KRnet" <krnet at list.krnet.org> wrote: > Paul, > > That particular configuration has a bit of a safety issue. You always > want at least one of your pumps before the gascolator. Check out any low > wing carburated Piper. The fuel flow goes from Fuel Tank -> Electric Fuel > Pump -> Gascolator -> Mechanical Fuel Pump -> Carb. > > The reason why you want one fuel pump before the gascolator is that even > the smallest leak in the gascolator will draw air under suction from the > pumps and starve the engine for fuel. If you have a pump before the > gascolator, you can turn on that pump to restore fuel flow. You may only > have a small seep or drip at the gascolator under pressure, but that's > enough of an air leak under suction to starve the engine. This was a > really common problem with the GlassAir series of aircraft. They were > designed with the gascolator under suction for the mechanical pump and had > chronic problems with fuel starvation thanks to an O-ring seal that didn't > seat well in their gascolator. > > Ideally, the first pump should not have to suck fuel up hill, which > eliminates the same problem should there be an air seep at a fuel line > junction between the tank and the pump. But the gascolator can be a real > problem because it is disassembled and reassembled regularly, so it's easy > to have an air seep on occasion. > > -Jeff Scott > Los Alamos, NM > > > Here is a picture of my first layout of my duel facet fuel pump design. I > got it from flycorvair.com. I ended up with something diferant with the > same pumps. > https://flic.kr/p/AoAMfe > > Paul Visk Belleville IL 618 406 4705 > Sent on the new Sprint Network from my Samsung Galaxy S?4 > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options >
