Shit, I remember when things were simple. I once got an abandoned car home by putting a gallon jug on the roof with a hose to the carb.Pressure is relative. In the EB, the pressure is vented into an evaporative canister, which condenses the volatile hydrocarbon fumes and sends it back to the gas tank as liquid gasoline. That system is still venting the pressurized air from the gas tank, and that air still contains small amounts of hydrocarbons, even though the majority has been condensed out.
On the flip side, manufacturers that make hybrids want to get all of the legal and tax benefits of making vehicles with the partial zero emissions designation. To get that status, your vehicle has to operate part of the time without the gasoline engine running and have ZERO evaporative emissions. The way to achieve that is by having a sealed gas tank that never vents to the atmosphere, except when refilling.
In the Prius, they use a rubber bladder inside of the gas tank, like a big water balloon, that has no air gap in the bladder, which means no evaporative losses.
In the Maverick, they skipped the expensive rubber bladder and went with a still expensive reinforced gas tank and filler mechanism that doesn’t leak fumes and won’t deform or rupture under pressure. The reinforced gas tank is still more expensive than the EB tank and it’s not needed to meet the less stringent base-line “low emission vehicle” standards that the EB has to meet.
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