Definition
A one-way valve installed in an aircraft hydraulic or pneumatic system that allows fluid or air to flow in one direction during normal operation while preventing reverse flow and the slow seepage that would otherwise occur past a standard check valve. It uses a tighter sealing arrangement than a conventional check valve to hold pressure for extended periods.
Plain English
A valve that lets fluid or air pass one way and seals tightly so it cannot dribble back the other way over time.
Context Anchor
Seen in aircraft hydraulic system discussions, especially where fluid must stay in a line or component when pressure is not being applied.
Derivation
Anti- (Greek, 'against') + leak. Named for what it is built to prevent: the slow, gradual reverse flow that an ordinary check valve might still allow.
Why Pilots Care
Prevents fuel or hydraulic fluid from draining back or leaking, preserving system pressure and reducing fire or failure risk.
Analogy
It works like a gate in a water line that stays shut against a slow unwanted trickle, but opens when there is enough intended pressure to move fluid through.
Intuition Check
Do not read “antileak” as meaning the valve fixes every possible leak. It only prevents a specific unwanted fluid movement through that valve path.
Example Sentence 1
The emergency brake accumulator uses an antileak check valve so that stored pressure is still available after the aircraft has sat overnight.
Example Sentence 2
During the preflight inspection the mechanic confirmed the antileak check valve in the fuel line was holding pressure correctly.