Definition
A flow-limiting device installed in a pneumatic line that uses a precisely sized throat to choke airflow at the speed of sound, holding the downstream flow rate constant regardless of further drops in downstream pressure. It protects pneumatic system components by capping the maximum mass flow that can pass through the line, even if a downstream line ruptures.
Plain English
A small fitting in an air line shaped to limit how fast air can flow through it. Once the air reaches the speed of sound at the narrow point, no more air can squeeze through, so the system is protected from runaway airflow if something downstream breaks.
Context Anchor
Seen in aircraft maintenance descriptions of systems that need controlled air or gas flow, such as pressure-measuring or pneumatic system lines.
Derivation
From 'sonic' (relating to the speed of sound, from Latin sonus, meaning sound) and 'venturi' (named after Italian physicist Giovanni Battista Venturi, who studied fluid flow through constricted tubes). The name describes what it does: a venturi-shaped restriction that operates at sonic speed.
Why Pilots Care
It supplies reliable vacuum to keep gyroscopic instruments accurate during climbs, descents, and power changes.
Analogy
Think of a narrow doorway in a crowded hall. Once it is jammed full of people moving through at maximum speed, opening more exits beyond it does not let people through any faster. The doorway sets the limit.
Grounding Statement
Once the gas reaches sound speed at the narrowest point, the venturi acts like a steady flow limiter.
Intuition Check
Sonic does not mean this part makes a sound. Here it means the air or gas reaches the speed of sound inside the venturi.
Example Sentence 1
The mechanic checked that the sonic venturi in the bleed air line was clear of debris during the pneumatic system inspection.
Example Sentence 2
During preflight the mechanic checks that the sonic venturi screen is clear so the vacuum-driven instruments will operate correctly.