What is the purpose of a dump valve?

What is the difference between a ricirculation and atmo?

If they provide a means of additional power, which should I
go for, I DON'T want one that makes that daft woosh sound.

Sorry if any of these questions are obvious, but hey!

 

As far as i know, they dont really give any considerable increase in power and the majority make that "daft" whoosh sound!

So if i was you, i wudnt bother!!