Definition
A T-shaped elastomeric sealing element used to prevent fluid or gas leakage between two mating surfaces, typically in hydraulic and pneumatic systems. The cross-section resembles the letter T, with the stem of the T fitting into a groove and the cap of the T pressing against the sealing surface. T-seals are usually installed with a pair of backup rings to prevent extrusion under high pressure.
Plain English
A rubber-like ring shaped like a T that sits in a groove and stops fluid from leaking past a moving or stationary part. It does the same job as an O-ring, but the T shape resists rolling and twisting under high pressure.
Context Anchor
Seen in aircraft maintenance instructions for hydraulic cylinders, landing gear parts, brakes, and other components that must hold pressure without leaking.
Derivation
Named for the shape of its cross-section, which looks like the capital letter T. The naming convention follows other shaped seals (O-ring, V-ring, U-cup), where the letter describes what you'd see if you sliced the seal in half.
Why Pilots Care
Maintains cabin pressurization and prevents water intrusion that could lead to corrosion or equipment damage.
Intuition Check
A T-seal is not a liquid sealant or tape. It is a fitted ring-shaped part installed inside a component to prevent leakage.
Example Sentence 1
During the landing gear actuator overhaul, the technician replaced the worn T-seal and its two backup rings before reassembling the piston.
Example Sentence 2
A cracked T-seal around the emergency hatch was discovered during the annual inspection.