Definition
A piece of test equipment used to measure how well the cylinders of a reciprocating aircraft engine hold pressure. It introduces compressed air into a cylinder through the spark plug hole while the piston is at top dead center on the compression stroke, and compares the pressure entering the cylinder to the pressure retained inside it. The difference indicates the condition of the piston rings, valves, and cylinder walls.
Plain English
A tool that checks whether an engine's cylinders are sealing properly by pumping air in and seeing how much leaks out.
Context Anchor
Seen during aircraft engine maintenance, especially during cylinder compression checks on piston engines.
Derivation
From 'compression,' meaning the squeezing of air and fuel inside the cylinder, plus 'tester.' The name describes exactly what it does — it tests how well the cylinder can hold that compression.
Why Pilots Care
Detects worn piston rings, leaking valves, or damaged cylinders that could lead to power loss or engine failure.
Analogy
It is like checking whether a bicycle tire holds air. If the air leaks out too quickly, the problem is not the gauge; something is not sealing properly.
Intuition Check
A compression tester does not make the engine more powerful. It measures whether a cylinder can hold pressure properly.
Example Sentence 1
After the mechanic ran a compression tester on each cylinder, he found one cylinder leaking past the exhaust valve.
Example Sentence 2
Low readings on the compression tester indicated that the valves needed adjustment on the Cessna's engine.