What must you remember with an air brake system with air-drier?

The combination of choices 1 and 2 is important because they ensure the proper functioning and reliability of the air brake system.

Choice 1 emphasizes the need to check the water-drainage valves of the air tanks regularly. This is critical as water accumulation can lead to malfunctions in the air brake system, compromising vehicle safety.

Choice 2 highlights the necessity of regular servicing of the air-drier, which is responsible for removing moisture from the compressed air. Keeping the air-drier in good condition prevents moisture-related issues that could affect braking performance.

In summary, both checking the water-drainage valves and servicing the air-drier are essential practices required by German traffic regulations to ensure that air brake systems operate effectively and safely. Choice 3, while relevant, does not form part of the correct combination in this case, as it is not as critical as the first two.