Definition
A safety device installed in a hydraulic line that automatically seals off the line when it senses an abnormal flow rate or excessive fluid loss, preventing the entire hydraulic system from draining if a downstream component or line fails.
Plain English
A small valve in a hydraulic line that shuts itself off if too much fluid suddenly starts flowing through it. This stops all the hydraulic fluid from leaking out when something downstream breaks.
Context Anchor
Seen in aircraft hydraulic system descriptions, maintenance manuals, and troubleshooting for leaks in systems such as brakes, landing gear, or flight controls.
Derivation
Borrowed from the electrical fuse, which breaks a circuit when current gets too high. The hydraulic version does the same job with fluid: it 'blows' (shuts) when flow gets too high, isolating the failure.
Why Pilots Care
Prevents a single line failure from draining the entire hydraulic system, preserving control surfaces and braking capability.
Analogy
It is like an automatic shutoff on a water line: normal flow is allowed, but if the flow suddenly becomes too high, the shutoff closes to keep the supply from being lost.
Intuition Check
A hydraulic fuse is not an electrical fuse and it does not melt. It is a fluid-flow safety valve that reacts to excessive hydraulic flow.
Example Sentence 1
When the brake line ruptured on landing, the hydraulic fuse closed and preserved enough fluid for the other brake to function.
Example Sentence 2
When the aileron actuator line ruptured, the hydraulic fuse isolated the leak so the elevator remained functional.