Definition
A cone-shaped spring washer used under a bolt or nut to maintain constant clamping pressure on the joint. As the bolt is tightened, the cone flattens slightly and acts as a spring, keeping tension on the fastener even when the clamped parts expand, contract, or wear.
Plain English
A slightly cone-shaped metal washer that works like a small spring. It keeps a bolt tight even when the parts around it shift with heat or vibration.
Context Anchor
Seen in aircraft maintenance, especially in parts assemblies where a fastener must keep pressure on a part despite vibration, wear, or small movement.
Derivation
Named after Julien Belleville, a 19th-century French engineer who patented the design. The aviation spelling 'Bellville' is a common simplification of the original 'Belleville.' Knowing it is a person's name explains why the term doesn't describe the washer's shape or function directly.
Why Pilots Care
Prevents critical fasteners from losing torque under flight vibration and temperature changes.
Analogy
Think of it like a very shallow metal cone that you press flatter. As it flattens, it pushes back, helping keep pressure on the parts around it.
Intuition Check
Do not assume this is just a flat washer used as a spacer. A Bellville Washer is designed to flex and push back like a spring.
Example Sentence 1
The mechanic replaced the Bellville washer under the brake stack bolt to restore proper clamping tension.
Example Sentence 2
After the run-up, the technician inspected the Bellville washers for signs of flattening.