Abstract: A device for the indirect, non-invasive and continuous measurement of blood pressure in a finger by using a photo-electric plethysmograph having a pressure cuff to be placed around the finger and to be filled with fluid, an associated light source and light detector, an electronic circuit, and an electric control valve having at least one fluid flapper-nozzle system, the cuff pressure being controlled by the plethysmographic signal in closed-loop operation such that the arterial volume is maintained on a pre-adjusted value and each deviation thereof due to changes in intra-arterial pressure is compensated immediately, whereby the control valve consists of a double fluid flapper-nozzle system in balance connection, whereby a single flapper member is positioned between the oppositely arranged nozzle openings of two nozzle members and alternately opens and closes these nozzle openings, one flapper-nozzle system being used in opposite sense, and one single chamber surrounding both nozzle openings being connected