Abstract: This valve adapted to be inserted between a ventricular catheter and a draining catheter comprises a body of flattened cylindrical shape enclosing a chamber having formed through its cylindrical wall an inlet passage for introducing the cephalorachidian fluid and an outlet passage for discharging this fluid. At the inner end of the inlet passage a frustoconical seat engageable by a ball valve acting as a non-return valve is provided, this ball valve being urged against the seat by a curved spring blade extending along the lateral inner wall of the chamber and mounted preferably in overhanging relationship on a diameter bar of magnetic material mounted in turn for concentric rotation on a pivot pin extending across the chamber. A tooth carried by the bar end opposite the spring blade is adapted to engage detent-positioning dents formed in the lateral wall of the chamber.