A one-way check valve:

Question

A one-way check valve is required to be between an air compressor and the first main reservoir. This valve prevents air from escaping the system if the air compressor develops a leak.

Accepted Answer

Prevents air from escaping if the air compressor has a leak.

Answer

Drains the water and compressor oil from the air tanks.

Answer

Activates the emergency brakes when there is a leak.