A pressure control valve is actually called a hydraulic choke. Its work is to control pressure during drilling operations and during a kick (blowout). The pressure is controlled with relative modification of the control elements, gate, and seat, by moving the gate. to control this, the choke is fitted with a hydraulic actuator with a double acting piston.
While drilling, one must know the control element position, the gate, towards the seat. All controlling information is shown at the drilling choke control panel, where the operator stands. The panel shows the gate displacement expressed in percents from the maximum value of the gate stroke.
Gate and seat are compound with tungsten carbide, reversible for double life period.