Whats special about FI catch cans

[Bartly]

So, I know there are plenty of threads that ask what is the best catch can. UPR and Bobs are always two in the rankings. Looking for one for my Procharger and see that Mak sells the UPR designated for the Procharger, and refer to it as a "dual valve". Looks like there is only one input and one output, so not sure why it's called a dual valve. I am wondering of there is something special about catch cans that would make one great for N/A and not so good for FI, and vice versa. I know the hoses plumb differently, just wondering if something internal to the can makes some of them behave better for FI.

Also wondering if there are really valves inside the cans as in "Dual Valve" catch can vs. "Single Valve". Looking at them it seems that there are just some baffling?

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