An externally controlled non-return valve which allows free flow in one direction with a non-return valve action and, in the other direction of flow, has a shut-off action which can be cancelled by means of control from outside has a valve cone 2 as the sole moving functional part. This valve cone 2 is not sealed off by soft packings. It has a collar 15 and a cylindrical extension 16 which, in conjunction with the housing 1 and the cover 3, form a differential area in the control space 18. This differential area is larger than the area of the bore 13 which forms the connection 26 so that, when the pressure in the control space 18 is relieved, a resultant force acts counter to the compression spring 5 and the valve cone 2 rises from the conical seat 14. Relief of the pressure in the control space 18 is performed by connecting the connection 20 to the tank by means of a pilot control valve 31. A land 22 formed because of the annular notches 21 and 23 gives rise with the fit of bore 17 in the cover 3 to a restriction which allows the valve cone 2 to close again only when the tank connection of connection 20 is sealed. The connections 25 and 26 lie on the valve axis and can be connected via the central bore 28 and the radial holes 30 of the valve cone 2 and the annular space 29, with the result that axial connection of connection fittings or control valves is possible and this is advantageous in terms of assembly. IMAGE
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