What is this??

I have noticed there's a strange part in my TC and I have no idea what it is or what it does. It is black plastic about the size of a baseball inside the front right fender near the horn and on the opposite side of the panel from the VAM. It has a vacuum line going to it and a check valve where it enters the tray on the firewall. What is this thing??
http://imageshack.us/a/img199/1905/cimg0810.JPG
http://imageshack.us/a/img841/8936/cimg0809w.jpg

Vacuum Canister. Stores vacuum under boost conditions. the HVAC uses vacuum to move the actuators and keeos them supplied with vacuum under boost conditions.

Interesting, I had no idea there was such a thing. I suppose it make sense though considering vacuum assist brakes and it sure would be annoying if the HVAC doors reset every time there was boost being made.