Definition
A device installed in a pneumatic or compressed-air system that removes liquid water and water vapor from the air before it reaches downstream components. In aircraft, moisture separators are typically found in pressurization, air conditioning, and pneumatic systems, where they protect equipment from corrosion, ice formation, and contamination by trapping condensed water and draining it overboard.
Plain English
A part that pulls water out of the air flowing through a system, so the air going downstream stays dry.
Context Anchor
Seen in aircraft air-conditioning, cabin air, and other air-system maintenance discussions.
Derivation
Moisture means water in the air, and separator means a device that pulls one thing apart from another. Together: a device that pulls water out of the air.
Why Pilots Care
Moisture left in pneumatic lines can freeze at altitude or cause corrosion and component failure.
Intuition Check
A moisture separator does not make air perfectly dry. It removes the water the system can separate out, especially droplets that form when air cools.
Example Sentence 1
During inspection, the technician drained the moisture separator to remove water that had collected since the last flight.
Example Sentence 2
During the preflight inspection the pilot confirmed the moisture separator was functioning so dry air would reach the instruments.