Abstract: A control device for a quick-closing valve of a steam turbine including a relief valve for reducing a hydraulic pressure opening the quick-closing valve, and a relief valve control valve arrangement having at least three valves which are hydraulically interconnected with the relief valve in such a way that the relief valve does not close the quick-closing valve unless at least two valves of the relief valve control valve arrangement are switched to a quick-closing position. The system includes a test control valve arrangement for selectively reducing and increasing the hydraulic pressure opening the quick-closing valve when the relief valve is closed.