Which component is necessary in an aircraft pneumatic system that uses an engine-driven compressor?

In an aircraft pneumatic system that employs an engine-driven compressor, a moisture separator is essential to the system's operation. The primary purpose of the moisture separator is to remove water vapor and other contaminants from the compressed air before it enters the pneumatic system.

When air is compressed, the increase in pressure can cause moisture in the air to condense. If this moisture enters the pneumatic system, it can lead to corrosion, freezing in cold temperatures, and overall inefficiency. The moisture separator captures this moisture, ensuring that the air supplied to various pneumatic components is clean and dry, thus maintaining optimal performance and prolonging the lifespan of the components involved.

While components like an oil reservoir, pressure switch, and relief valve can be important in various contexts and systems, their roles differ from that of a moisture separator in terms of addressing moisture removal, which is critical in maintaining the integrity and functionality of the aircraft's pneumatic system.