Abstract: An apparatus for controlling the flow of an infusion fluid in an infusion system with a drip chamber and a deformable tube, is provided with a sensor for detecting the drops of infusion fluid falling in the drip chamber, means for seting a desired flow rate, pinch clamp means for pinching off the deformable tube and a processing unit for controlling the pinch clamp means is dependence of the set desired flow rate and the signal of the sensor. The pinch clamp means is movable with a variable speed between a rest position in which the tube is fully released, and a closed position in which the tube is fully closed. The speed in a controlling range preceding the closed position is substantially lower than the speed adjacent the rest position.