Oil and gas production handbook An introduction to oil and gas production

Variable flow choke valve. The variable flow choke valve is typically a large 
needle valve. Its calibrated opening is adjustable in 1/64 inch increments 
(called beans). High-quality steel is used in order to withstand the high-
speed flow of abrasive materials that pass through the choke, usually over 
many years, with little damage except to the dart or seat. If a variable choke 
is not required, a less expensive positive choke is normally installed on 
smaller wells. This has a built-in restriction that limits flow when the wing 
valve is fully open.