Check Valve: Installing
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2013 Audi S4, 2013 Audi A4, 2012 Audi S4, 2012 Audi A4, and 2011 Audi S4. However, it is still accessible from the selected car via links, so may be relevant.
-- Installation is performed in reverse sequence. Observe the following when doing so:
Valve must allow air to flow in direction of arrow.
the arrow indicates the direction of the vacuum pump.