Exhaust riser valves

[DjArgyleFan]

On both exhaust risers on my 4.3GL Volvo V6 there is a valve with a pipe going to the air filter. Can anyone tell me what they actually do and if they should blow into the air filter or suck from it? Also any ideas on what would happen if I didn't put them back and left a blanking plug in their place. Thanks as always for any help/advise/thoughts.
Martin.

 

[Don S]

Re: Exhaust riser valves

They are vacuum breaks. They help prevent the exhaust from sucking water in (especially at idle) due to valve overlap.