Abstract: Valve unit, particularly for high-pressure pumps, comprising a cage mainted in position by a screwed plug and containing a valve disc and a valve seat, the screwed plug having a threaded shank provided with an annular groove for a seal gasket in contact with the inner wall of the cavity which receives the valve unit, said annular groove for receiving said seal gasket being positioned adjacent to that end of said thread close to the valve unit, and being inserted into a portion of the plug receiving cavity having a diameter less than the outer diameter of the plug thread.