Final answer:
The normal position of a non-operating brake valve is represented by the code (23-99), indicating a closed or inactive state.
Step-by-step explanation:
The normal position of a non-operating brake valve is represented by the code (23-99). This refers to the valve being in a closed or inactive state. In technology, brake valves are often used in pneumatic systems to control the flow of air and activate or release brakes. Depending on the system, different codes or positions may exist for indicating open or active states of the valve.