Definition
A valve in a hydraulic system that automatically shuts off the flow of fluid to non-essential subsystems when system pressure drops below a preset value, ensuring that essential subsystems continue to receive adequate pressure and flow.
Plain English
A valve that decides who gets the hydraulic fluid first when there isn't enough to go around. If pressure drops too low, it cuts off the less important systems so the critical ones (like brakes or flight controls) still work properly.
Context Anchor
Seen in aircraft hydraulic system descriptions, especially where one pressure source feeds both essential and nonessential equipment.
Derivation
From Latin 'prior' meaning 'former' or 'first in importance.' The valve enforces priority — essential systems first, everything else second.
Why Pilots Care
It keeps critical functions such as flight controls, landing gear, and brakes working even if hydraulic demand spikes or part of the system is compromised.
Analogy
Think of a priority valve like a person handing out limited water during an emergency: drinking water is supplied first, and washing water waits until there is enough left over.
Intuition Check
Do not read priority as simply meaning the valve opens first. In this term, priority means the valve protects the more important part of the system when pressure or flow is limited.
Example Sentence 1
When the hydraulic pressure dropped during the leak, the priority valve closed off the cargo door system so the flight controls kept full pressure.
Example Sentence 2
During a hydraulic leak in a non-critical line, the priority valve maintains pressure to the brakes so the airplane can still stop safely.