Method for diagnosing the state of wear of a valve arrangement for controlling the flow of a process medium

A method and valve arrangement are provided for controlling the flow of a process medium through a pipeline. A pneumatic actuator moves a valve element, which is accommodated in a valve housing, and switches the flow of the process medium, in accordance with a positioning control system by means of a control piston, to at least one side of which control pressure is applied in a drive chamber. An electronic evaluation unit connected to the positioning control system monitors the operating state. A pressure sensor measures the pressure in the drive chamber, and the evaluation unit analyzes the measured pressure value with respect to a pressure p and the pressure change dp(t) over time to determine the flow into/from the drive chamber and/or the ratio (V/A) of the drive chamber volume to the effective opening cross section of the valve arrangement as a measure of the operating state of the valve arrangement.