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Fuel vent check valves - how to inspect and/or repair

Hello; I'm diagnosing a potential fuel vent siphon leak and I have verified that all of the vent tubes are unobstructed, so it appears that I should next inspect the check valves. If I were to remove these and open them up, is there anything I can do to overhaul or repair them? They do not appear to be available for purchase new any longer.

Model: Bonanza E33A
Aircraft Serial Number: CE-277
Posted 6/18/2023 - 8 months ago
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Hold the valve in your had, note the arrow. Air will pass in the direction of the arrow and will not pass counter direction. Mouth pressure is enough, an air compressor may cause damage. They can be disassembled to clear bug nest or free a stuck valve, but no real user serviceable parts. When reinstalling, arrow points to the fuel cell and one flat of the valve has the word 'hinge' marked on it; that is oriented to face the upper wing skin.

Mike
ABS Tech Advisor

Posted 6/18/2023 - 8 months ago
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The check valves have an arrow that should point towards the tank when installed. The word HINGE is engraved on one of the wrench flats on the valve. HINGE should be on top and arrow pointed towards tank when installed.
Once you have valve out blow through the valve in arrow direction to ensure it will open. Blow out the line attached to the valve that goes to small hole on lower wing surface.

Bob Ripley
ABS Technical Advisor

Posted 6/18/2023 - 8 months ago
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Thanks all for the comments. I could not force air through the check valve so I disassembled it and found that the flapper was bonded to the opening - probably from disuse. I managed to free it and clean the sealing surface and lubricate it to prevent further stickage. It's reinstalled and working properly.

Of note, the only real serviceable part in here is the main o-ring for the cylinder when unscrewing the two halves. I did not have a replacement and the o-ring was in good shape so it was reused.

Attached are a few photos of it disassembled as I have not yet seen any out there in the ether.

Some folks like to put a little Marvel Mystery Oil in their fuel from time to time. MMO is good stuff, but it will glue a fuel line check valve closed.

Posted 6/26/2023 - 8 months ago
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If you are going to put MM Oil in anything put it in the engine oil. I put 1 Qt. of MM Oil in the tank at each oil change and I believe that that routine has prevented any stuck valves or stuck piston rings in the piston grooves for quite a few years in my G-35 V tail.

Regards, Lew Gage

Posted 6/26/2023 - 8 months ago
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Fuel vent check valves - how to inspect and/or repair