Technical name for this?
 

B4184s2 engine. S40 non turbs.

What's the technical name for the device that the two vacuum hoses attach to on the lid of the air filter box? There is a flesh coloured bulbous device inside with a brass centre. What's it's sole purpose and how do I check to see if it's working correctly? I have drawn in air by sucking the through the hoses and it gives off a clicking/diaphramatic noise. I did this also to activate the flapper door in the bottom hose, I could hear the flap moving back and forth.