Definition
A valve fitted to the lowest point of an internal supercharger case that allows fuel and oil to drain out when the engine is shut down. The valve is held closed by air pressure when the supercharger is operating and opens automatically when that pressure drops, preventing residual fuel or oil from pooling inside the case where it could cause a hydraulic lock or a fire on the next start.
Plain English
A small automatic valve at the bottom of the supercharger that drains away leftover fuel and oil after the engine stops, so nothing dangerous can collect inside before the next start.
Context Anchor
Seen in aircraft engine system descriptions, especially for reciprocating engines that have a built-in supercharger.
Derivation
Internal because the supercharger sits between the carburetor and the cylinders, inside the induction system. Drain valve because its job is to let liquid drain out by gravity when the engine is no longer running.
Why Pilots Care
Prevents liquid buildup that could damage the supercharger or cause engine failure.
Intuition Check
This valve does not drain air pressure from the supercharger. It drains liquid that has collected inside the supercharger area.
Example Sentence 1
After shutdown, the internal supercharger drain valve opens to release any fuel or oil that has settled in the case.
Example Sentence 2
Before flight, the pilot confirmed the internal supercharger drain valve was functioning to avoid any liquid accumulation.