US Patent 7213609 Control system for high pressure oil wells

A pressure reducing valve assembly for a high pressure oil well comprised of a hollow housing and a metering assembly disposed within such housing, such metering assembly comprising an entry liner having an entry bore, an exit liner having an exit bore, and a rotatable metering cam comprising at least one metering port that connects the entry bore to the exit bore. The metering port forms adjustable orifices with the entry bore and the exit bore, and effects the reduction of pressure within the metering assembly, thereby providing a variable choke of the fluid flow therein. The metering port is adjustable, and preferably replaceable with at least a second metering port by with a simple rotation of the metering cam.