Definition
Coiled springs fitted around the stem of each intake and exhaust valve in a reciprocating aircraft engine. They hold the valve firmly closed against its seat and return the valve to the closed position after it has been opened by the camshaft and rocker arm. Most aircraft engines use two concentric springs of opposite winding direction on each valve to prevent surging and to provide a margin of safety if one spring breaks.
Plain English
Springs that snap each engine valve shut after it has been pushed open, keeping the cylinder sealed at the right moments.
Context Anchor
Seen in piston-engine maintenance, cylinder inspections, and explanations of how aircraft engine valves open and close.
Why Pilots Care
Weak or broken valve springs cause valve float, loss of compression, rough running, and potential engine damage at higher power settings.
Analogy
Like the spring on a screen door that pulls it shut after someone walks through — without the spring, the door would just hang open.
Intuition Check
Do not think of valve springs as the parts that open the valves. Their main job is to close the valves and hold them closed at the right time.
Example Sentence 1
During the engine overhaul, the mechanic replaced all the valve springs to ensure consistent valve closing pressure across every cylinder.
Example Sentence 2
High-RPM operation can cause valve float if the valve springs are no longer strong enough to close the valves quickly.