If your truck or bus has dual parking control valves, it means that you can use pressure from a separate tank to: | Semi-Truck or Big-Rig Drivers (CDL) General Knowledge Test | Drivers License Practice Tests

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If your truck or bus has dual parking control valves, it means that you can use pressure from a separate tank to:

Balance the service brake system.

Release the spring brakes to move a short distance.

Apply more brake pressure if the main tank is getting low.

Stay parked without using up service air pressure.