Yes, they require some amount of suction to open. And that's about as accurate of a statement as you're going to find on the subject . I've read up on the regulations that specify when you need one (essentially when the fuel line is below the top of the tank), but have never seen anything about the opening force required for one to operate.
. I've read up on the regulations that specify when you need one (essentially when the fuel line is below the top of the tank), but have never seen anything about the opening force required for one to operate.
