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Main Filter Bypass Fuel Line

R7237

Well Known Member
Building my 12iS as an EAB and working on the fuel system. The plans call for fabricating F-12127E as the Main Filter Bypass Fuel Line mounted near the fuel pump. This line has a check valve and bypasses the main fuel filter (10 micron). I am unsure why this is done. I understand that if you had a problem with the "fine filter", this would still allow fuel to "bypass" the filter and make it to the engine and therefore particulate matter greater than 10 microns into the injectors. I don't think this is routinely done on most aircraft fuel systems... Am I missing something? and should I include this on my EAB fuel system? Thanks in advance.
 
Before you consider making any design changes to the fuel system (yes, allowed under E-AB) I suggest you get familiar with the 912iS install manual.
This by-pass is specifically required by Rotax and is specified in that manual.
 
Before you consider making any design changes to the fuel system (yes, allowed under E-AB) I suggest you get familiar with the 912iS install manual.
This by-pass is specifically required by Rotax and is specified in that manual.

That makes sense. The only reason for the EAB is the use of the ULPower engine. Thank you very much for the quick response. Was trying to keep it as close to the specs vans recommends and didn't understand the reason for the bypass. I very much respect Vans design and am a repeat offender, I just felt the ULPower engine was a better fit for my application. Thanks.
 
That makes sense. The only reason for the EAB is the use of the ULPower engine. Thank you very much for the quick response. Was trying to keep it as close to the specs vans recommends and didn't understand the reason for the bypass. I very much respect Vans design and am a repeat offender, I just felt the ULPower engine was a better fit for my application. Thanks.

Are you going with the 260 or 350 ULPower version?
 
Are you going with the 260 or 350 ULPower version?

350iS with option 50 amp alternator
If you go this route, this is the fuel pump I am using
https://www.flyefii.com/products/accessories/dual-electric-fuel-pump/
and I am mounting it is the same location as the Fuel system for the Rotax912iS. I am using PTFE SS braided fuel lines, and a Holley 100 micron pre filter, otherwise it is the same setup,,, other than the return fuel line bypass is on the engine and not in the center channel like it is on the 912iS.
 
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There's a few more around here, I think rgawer built one too.

130HP in a RV-12 is a pretty potent combo, I would think. Might have to watch the airspeed a bit more carefully?
 
There's a few more around here, I think rgawer built one too.

130HP in a RV-12 is a pretty potent combo, I would think. Might have to watch the airspeed a bit more carefully?

I have had the opportunity to fly in one (RV-12 with 350iS ULPower) and that is what sold me on the idea. I think it is the perfect combination of engine to airframe. That Rotax 912iS is just a bit complex for me. I think it is a great engine with a track record of the 912, but didn't like the cost of ownership. And if you ever reach overhaul, you buy another one. When I added up everything from "gearbox" service, to "rubber" service, it was a no brainer for me.
 
Yes this bypass is no special vans design. It is from the installation manual. But it is not to find in older versions of this document and it is not without questioning among builders. It is supposed to open up at 1,2 bar. That equals a water cylinder of 30 feet hight. If the filter has gotten that dirty, I don't want it to be bypassed. I would be affraid the injectors would not like the highly contaminated fuel and the engine would quit soon after opening. I would rather have the filter working a bit longer and recieve a warning. Therefor the fuel pressure sender has to be placed befor the filter. The fuel pressure regulator keeps the pressure behind the filter at 3,0 bar. Anything more the sensor reads at the input side is the pressure drop in the filter. If it exides lets say 1,0 bar, the garmin, dynon, mgl can give a warning.
 
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