Gate valves are on/off control devices used during drilling, completion and production of oil and gas wells. They are designed to be operated in either the fully open or fully closed position. Gate valves are not chokes and should never be used for throttling.
Gate valves are positioned primarily in two places on conventional wellhead assemblies; in the wing position of casing heads, casing spools, or tubing spools; or in a Christmas tree assembly
Generally speaking, gate valves that are installed in the wing position of the lower sections of wellhead assemblies, are called annulus valves
The valves that are installed on the upper sections of wellhead assemblies, are called Christmas tree or production gate valves
These valves can be either manually operated or mechanically actuated