The primary function of a choke valve is for flow restriction. Choke valves are highly susceptible to erosion / flow damage by the nature of their operation, particularly where solid particles are present in the process medium.
Choke valves are not designed to reduce pressure.
The operation of a choke valve is generally by a hand wheel device screwing down a stem, which is connected to a “flow limiter” device (for example a cylinder with a hole in it).
As the cylinder rises and falls in the sleeved bore, the cross sectional area for flow increases or decreases accordingly. Choke valve occasionally have “full closure” capability.
source: score-europe