Fuel Cell Venting
We are taught to check fuel vent lines for insect nests or other debris. You should also check the caps to be sure they are vented properly and tight. Not all caps are vented, for example all Comanche gas caps are non-vented. An Aztec cap, which is vented, looks like a Comanche cap and will fit a Comanche, so you need to be careful when replacing caps.
Fuel Caps
“Monarch Premium Caps are a stainless steel umbrella cap with a ratchetting mechanism that releases and “clicks” when the cap is tightened correctly. They have a dual spring-loaded vent for both pressure and vacuum. This is a secondary vent in case the primary vent gets obstructed.”
Check the vents, if your cap has them, and pay special attention to the gasket and any rubber parts. I lost part of the umbrella gasket on mine which meant that it wasn’t operating properly.
Apple Valley Crash
Postcrash inspection of the engine revealed no discrepancies. Inspection of the fuel system revealed that the left auxiliary fuel cell vent lines were plugged by insects and mud at two different internal locations.
Fuel Vent Lines
There is an abandoned jet next to my Cherokee and wasps have taken up residence. I have found wasps in my engine compartment and in the rudder, so I am extra careful when pre-flighting to make sure that they have not decided to make nests in the fuel vent lines.
Fuel cell vents have a check valve in them to prevent water and contaminants from getting into the fuel cell. The Cessna 210 vent line has a pinhole on the bottom. This allows moisture to drain and helps avoid having ice clog the line.
Cessna 210 Fuel Vent Line—One on each wing.
Piper Cherokee Fuel Vent Line—One on each wing.
Cessna 182 Fuel Vent Line—One for the whole system.
Peter B. Hi11 uses old tennis balls as vent covers on his Cherokee. After a small slit with knife or razor blade, one will fit perfectly over the pitot sword. The other two, after the puncture of a small hole, will fit snugly over the fuel tank vent overflow pipes,prevent insect blockage, and subsequent fuel starvation (which has been the sad fate of several Cherokees over the years).
This is the fuel vent system from the Cherokee parts manual. Notice how the vent line starts at the top of the fuel cell and vents out the bottom of the wing. You can also see the umbrella vent in the fuel cap.
