You dont need to worry about atmospheric dump valves matey, recirv valves let air escape back into the airway into the engine so the turbo doesnt stall.
 
in simple terms its the dump valve that goes ttttsssshhhhh!
 
They are the valves that dump the air out into the atmosphere from turbo, making the whooooshy sound. Although heard they dont work well with the leon engine?
 
if you want one, the closest thing you can get is the forge splitter (what ** got)
 
The Forge FM CL 007P valve
You can see it here in this link http://www.forgemotorsport.co.uk/content.asp?inc=product&cat=1703&product=FMCL007P
The Forge valve is a two piece single piston , single spring type valve ,that will locate in the same factory position as your Bosch valve .This valve is guaranteed for life and can serviced if required.when the valve the valve is fitted with a CAI , it can be heard venting
through the intake. http://www.forgemotorsport.co.uk/content.asp?inc=product&product=FMIND01

We have the valves in stock in polished and black and carriage is £ 8.00. The valve will be fine on your car as standard and should also be ok on a chipped car however we can upgrade it to a stronger spring if necessary.

The other option is our New Forge Split R valve
http://www.forgemotorsport.co.uk/content.asp?inc=product&cat=1703DV&product=FMDVSPLTR
This is designed to work on all 1.8T engines and again when fitted with a CAI it will sound even louder
 
Cold Air Induction / Intake.

Technically, a CAI kit is an induction kit that has the filter mounted down low behind the bumper to ensure it gets lots of cold, dense air.

But the term CAI has also been used to describe a cold air feed, so a dedicated feed to provide cold, dense air to the filter.