Fuel filter location- Long Story first -Summary last.
I was 5,000 ft AGL over Oklahoma on my way to Texas when my engine shut down then started surging full power to nothing, full power to nothing. It would only run at about 1200rpm smoothly and I was losing altitude. I switched tanks back and forth furiously with the sputtering continuing, just bursts of power coming from the engine. I made it 12 miles to 3,000 agl over an airport, and continued diagnosing the problem. I took the fuel selector, and just SPUN it all the way around 360 deg and that brought the engine back to life like nothing had happened. I made an uneventful landing and cleaned out the gascolator and fuel selector valve. Evidently a small drip of Proseal had made it's way into the fuel selector valve and lodged itself in the fuel selector's passages. It's a Van's selector on my 1990 RV-4. I found the 1/4" x 1/2" by .020" drip in my gascolator, which is after the selector valve and boost pump (it passed through the facet type pump), and before the engine driven pump. The gascolator is really only protecting half the fuel system at that location. That Proseal drip could have been a flake of paint, a leaf, a twig, a rivet, a blade of grass, a bug that was crammed into the tank vent, anything.
The best place in my opinion for a fuel filter is right in the fuel tank in the form of a finger strainer. The next best place is between the tank and the fuel selector valve. So I added two plastic/paper filters with rubber clamps and hoses between my fuel tanks and my fuel selector. In fact, most of the paper filters will not allow something 1/8" dia by 1/2" long to get INTO the filter because it would have to make a sharp turn against the paper filter's metal boss. That's why I run my paper filters backwards, with the opening to the paper towards the tank, with the flow arrow pointed towards the tank. (Yes they cannot be visually inspected but they will not block up easily). This way, if anything can fit in the fuel line it will flow unimpeded directly into the inside of the paper filter and keep the fuel line open. I have learned this from prior experience on another plane, during an inspection I found a 1/8" diameter 1/2" long piece of epoxy stuck in the inlet to the fuel filter because it could not get into the fuel filter. (That did not cause an engine out). That's when I started running them backwards to let larger objects that can make their way into the fuel line go right into the center of the fuel filter and stay there, safe and sound. Now my fuel selector valve is clean, my boost pump is clean, and the only thing left unprotected is the fuel tank outlet. Something could wedge in the outlet's opening but the tanks are sealed and completed. Next time I'm in the tanks they'll get finger strainers. I think with one fine mesh finger strainer at each tank outlet the rest of the system would be fine. All the junk would stay in the tank and float around but it wouldn't get into a fuel line. One thing good to do at annual is to siphon the tanks using a 3/4" urethane hose, and work it around the corners to clean the tanks out of any floaties. It's amazing what gets in the tanks. Careful of the finger strainers if you have them, they bend easily with rough treatment.
There are some high quality looking filters sold at auto parts stores, they can be disassembled for cleaning and have replaceable mesh filters, they are chrome plated and have 1/4" barb fittings. I don't like these because the fuel must pass through two 1/8" diameter holes at 90 deg angles and larger items will not get into the filter at all but will stick in these smaller openings and block the fuel flow.
It could be argued that any pump or valve or pressure sender or flow sensor that can disintegrate in the fuel system should have a fuel filter right after it to catch debris and keep it from getting into the rest of the system. So one filter in each tank, one after the fuel selector, one after the boost pump, one after the engine pump before the carb. (Or inside the carb inlet like the MA carbs have).
The 5,000 AGL altitude I had allowed me to get to an airport and figure out what the problem was, and let me avoid an off-field landing. Had I been at 2,000 AGL I would have had to land off-field right away.
Lessons I learned:
1. Fly at 5,000' AGL when practical.
2. Spin the selector valve 360 degrees to clear it.
3. Put filters before the selector valve.
4. Paper fuel filters installed in the reverse flow direction allow larger debris to be trapped without blocking the line. You can't see the junk in there but if it gets in there while flying you can't see it anyway and you can't clear it while flying so keeping it clear is the most important thing. Check or replace them at annual. They do hold a lot of stuff compared to smaller units.
5. Nice shiny chrome plated fuel filters can be easily blocked at the inlet port due to the 1/8" holes inside the filter before the element.
6. I practice using the NEAREST function of my GPS and was able to get over an airport in a few short minutes. I also practice what to check when the engine goes quiet.
Where I had it installed was about as good as it'd get for convenience... Don't know if anyone else knows of other pros/cons regarding various locations.. My preference would be to keep it in as-cool-as-possible location.. so would stay away from firewall etc.. And would avoid unnecessary parts (ie having two when only one is needed...) Just my preference...
