Definition
A one-way valve installed in the delivery air duct of a turbine engine's pneumatic or bleed-air system that allows compressed air to flow in the intended direction only and prevents reverse flow back toward the source. It is commonly fitted between bleed-air sources, cross-bleed manifolds, or between an engine and a shared duct so that air from one engine or source cannot back-feed into another.
Plain English
A valve in an aircraft's compressed-air ducting that lets air flow one way and blocks it from going backward.
Context Anchor
Seen in aircraft pressurization, heating, ventilation, and air-conditioning system descriptions or maintenance checks.
Derivation
Check' here means 'to stop or restrain,' from Old French eschequier. A check valve is named for its job of checking — stopping — flow in the unwanted direction. The rest of the name simply identifies which duct it sits in: the one delivering air.
Why Pilots Care
Prevents damage to upstream components and maintains correct airflow direction for engine and cabin systems.
Analogy
It works like a one-way pet door: it lets movement go one way, but closes when something tries to come back the other way.
Intuition Check
“Delivery” does not mean package delivery here; it means the duct carries supplied air to where it is needed. “Check” does not mean an inspection here; it means the valve stops backward flow.
Example Sentence 1
The delivery air duct check valve prevents bleed air from the running engine from flowing backward into the engine being started.
Example Sentence 2
With the delivery air duct check valve operating correctly, compressed air reached the cabin without reverse pressure issues.