Vacuum Pipes
WARNING: This page is about a different car, the 2018 Jaguar XE and 2017 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.
Plastic pipes connect the brake booster to the intake manifold and the vacuum pump to provide the vacuum for the brake booster. The connection with the brake booster contains a check valve to maintain the vacuum in the brake booster. An inline check valve near the connection with the intake manifold prevents air being drawn from the intake manifold and fuel vapor from entering the pipes.