This picture show a very nice installation of the main Viking to RV-12 lower engine support structure.  

Looking at the background fuel system parts, some comments are needed.

Slightly right of bottom center, there is an Andair gascolator mounted to the firewall.  The Viking engine is fuel injected and hence have a full return fuel system.  As soon as a fuel pump is activated, prior to engine start, fuel is circulating and any benefit of the gascolator to trap water is lost.  Fuel sampling should be at the fuel tank instead.  

This gascolator is just a heat sink, absorbing heat from the engine exhaust and radiator / oil cooler air, due to its location.  This is likely to boil the fuel, creating a vapour blockage to the fuel pump inlets.  Recovery would only happen after the engine shuts down from lack of fuel, the airplane descends for a while without engine power to cool the gascolator and fuel pressure is regained.  

Ideally, there should be no low pressure fuel in front of the firewall and the fuel pump inlets should be below the fuel tank bottom.

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Comments

  • Good catch! I plan to heat shield that gascolator (as well as all fuel lines and fittings).
    It's an ANDAIR GAS375 high pressure/high flow model. I chose it not so much to trap water, but as a fine particle, high flow filter prior to the pumps. Internally it incorporates a large area stainless steel filter screen that is folded/pleated around the vertical axis. The screen area is 24 square inches, and It filters to 70 microns. The assembly is fully O-ringed, and will tolerate suction in high pressure fuel systems like ours. Kinda pricey though ($400).
    On pre-flight I plan to sump it looking for dirt, trash, pro-seal bits, etc. If I need to clean it, it's easy to reach and doesn't dump its contents inside the fuselage tunnel like my former setup did.
    As for water, I also installed the tank sump under the rear tunnel as you suggested, so I can sump for water there.
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