Choke valve

In internal combustion engines with carburetors, a choke valve or choke modifies the air pressure in the intake manifold, thereby altering the air–fuel ratio entering the engine. Choke valves are generally used in naturally aspirated engines to supply a richer fuel mixture when starting the engine. Most choke valves in engines are butterfly valves mounted upstream of the carburetor jet to restrict air flow there and produce a higher partial vacuum downstream, which increases the fuel draw.

In heavy industrial or fluid engineering contexts, including oil and gas production, a choke valve or choke is a particular design of valve with a solid cylinder placed inside another slotted or perforated cylinder.