Cessna 120-140 Association

"The 140a system should normally vent through the tube in the center of the cabin, so, even if both caps failed to vent there should be no pressure."

Yes, as John states "normally" but since there is the chance that the vent on the cabin roof could potentially get plugged they ( FAA) said you need a backup vent, that why the one way valve fuel cap. One way meaning will let air in, but not fuel out.

Also to clarify, that cap that you show in the picture is only required on an A model, if you don't have an A model which by the serial number I'm sure you don't, then you have the wrong fuel caps.

As John said, you really need to figure out what is going on there....

...probably not at issue here, but there have been a few owners who have "modified" their tanks and venting (...connecting, changing the selector and caps) over the years sans "approval" without realizing the potential for disaster. Mac

Well John,
you were correct sir. Seems I was opening the same tank first every time, releasing the pressure (positive).
Yesterday I verified that both tanks had positive pressure. I attached some pics of my actual fuel caps and selector.

Thanks again for all the help.

Those are the wrong caps, those caps are specific to the A model. The proper caps will allow venting in both directions.

Got it Blaine.
Thanks again for the info.

Rick, you could do as John suggested and remove the silicone valve so it vents in both directions, however the caps you have are quite valuable if you check what the new price is on ACS or even the used prices on eBay. You might be better trying to find the proper caps as depicted in the Neil Wright article and sell those caps. Just a thought.....

Sounds good Blaine.

I am waiting to hear from another C140 owner close to me (next airport north) who might have a set he previously replaced.

So, you have the earlier system designed for "Both" operation. I agree, the caps with the holes are bullet and idiot proof.

might have a set he previously replaced.

With what? His best bet may to put them back on his plane!

He was not able to find them so I just ordered a set from Aircraft Spruce.

Meanwhile I have lots of time to address years of neglect on this finish...

oh boy Rick, if you think thats years of neglect I would not want to send you pictures of my airplane I hope one day to get mine as shiny as yours.