The purpose of the dump valve in a pressurized aircraft is to relieve?

The purpose of the dump valve in a pressurized aircraft is indeed to relieve all positive pressure from the cabin. This function is critical for maintaining safety and comfort within the cabin environment.

In the event of a rapid decompression or when the aircraft is preparing for landing and the cabin pressure needs to match the outside atmospheric pressure, the dump valve allows the cabin pressure to equalize quickly. This ensures that the passengers and crew can safely adjust to the changing pressure conditions without experiencing significant physiological effects, such as barotrauma or hypoxia.

The other systems mentioned, like the fuel, hydraulic, and external pressure sources, do not utilize the dump valve for their pressure management. The design and function of the cabin pressure system specifically focus on the comfort and safety of the occupants, which is why the dump valve plays a crucial role in that context.