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I have two vented fuel caps, one in use and a spare, and they are both the same internally-neither has a small spring or loose plastic valve part. They both have two `valves` (but they are are fixed in) and mounted `one up-one down`!
I`ve no idea how it all functions and it all seems weirdly complex.

Not mentioned, but the vented cap is for UK set up and the not vented is for N/A emissions (it is vented through the charcoal cannisters). It was to keep any fuel tank vapors from reaching the atmosphere. For other countries, it depends on what version you got (probably mix and match, vented/non vented, knowing BL). A friend souped up his 2 liter and when he was on a run after while the car would stumble and stop. After sitting on the side of the road for a while, it would work fine. He thought it was the electronic ignition acting up when hot but he had removed the charcoal cannisters and sealed it off. When enough fuel in the tank was used, enough vacuum built up to overpower the pump and the engine would cut out. All he had to do was open the fuel filler cap to allow air in and he could have continued on his way. He got a vented cap and it was fine after although he could smell fuel from time to time.

An interesting adjunct (nothing to do with the 7), my Volt has a sealed pressurized gas tank to prevent the lighter components from evaporating). When you go to put gas in, you press a button, Venting fuel tank comes up on screen for a couple of seconds, then it says, OK to add fuel. Since a lot of them might not need gas for a year, it prevents the lighter components from evaporating, then it says enough is enough and makes you use gas when you use the car to burn it off so you can put fresh fuel in. If you do add a few gallons every so often you never get to see it (called FMM or Fuel Maintenance Mode). It does have an engine maintenance mode every 6 weeks to circulate fluids/oil but that only burns .1 to .2 liters, not enough to require putting in gas every year (if your travels are with in the battery range). I rarely see that either because I use about 5.8 liters every month when I go to the car club meeting although that didn't happen during COVID.