A valve block disposed adjacent a tool attachment of a working machine, where the tool attachment is adapted for connection to different types of hydraulically maneuvered tools or implements with the aid of a hydraulically actuated locking device. The valve block includes first port means, second port means, and third port means for connecting hydraulic lines of the working machine to hydraulic coupling elements and to the locking device respectively. The valve block includes a line system and valve means which communicate with the port means so as to fulfill at least three of the following five functions: ensuring the presence of pressure in the locking device in the event of a fracture in the hydraulic lines of the working machine; ensuring connection of the first port means with either the second port means or the third port means to obtain post-tensioning of the locking device to relieve the pressure load; and to provide pressure limitation.