Definition 1 of 2
Definition
A valve used in aircraft fluid systems (fuel, hydraulic, or pneumatic) that allows the pilot or system to direct flow from a source to one of several possible destinations, or to choose between several possible sources feeding a single line. Common examples include the fuel selector valve, which chooses which tank feeds the engine, and hydraulic selector valves, which route pressure to operate landing gear, flaps, or brakes.
Plain English
A switch-like valve that lets you choose where fluid goes or which source it comes from. In a fuel system, it picks which tank feeds the engine. In a hydraulic system, it routes pressure to the component you want to move.
Context Anchor
Seen in fuel system controls, aircraft system diagrams, and maintenance procedures where flow must be directed from one place to another.
Derivation
From 'select' (to choose) and 'valve' (a device that controls flow). The name describes its job: a valve that selects.
Why Pilots Care
Correct operation ensures hydraulic pressure reaches the intended actuator or fuel reaches the selected engine or tank, directly affecting landing gear extension, flap movement, and engine operation.
Intuition Check
Do not think of a selector valve as only an on/off valve. Its main job is to choose between available paths or sources.
Example Sentence 1
Before engine start, the pilot moved the fuel selector valve to the fullest tank.
Example Sentence 2
During the preflight, the mechanic checked that the fuel selector valve moved smoothly between the left, right, and both positions.