A "plug and play" process control valve 10 providing closed loop feedback control has a built in microprocessor 40, stepper-motor 20, a position encoder, a valve body having an inlet 11 and an outlet 12, and pressure sensors 30, 31 positioned within the inlet 11 and the outlet 12 of the valve body, the pressure sensors being connected to the microprocessor 20, which is in turn connected to an input from the position encoder, and provided with outputs to the stepper-motor 40. Within the valve body there are a pair of apertured ceramic shear action discs 13, 14. The stepper-motor rotates the upper disc 14 relative to the apertured stator disc 13 to control pressure or flow in the pipeline.