<p>A change-over valve for hydraulic walking mine-roof supports comprises a valve housing containing a sealed-off operating piston in which a valve member supported on a helical spring is displaceably arranged, the piston being responsive to the supply of small quantities of hydraulic fluid through an end connection in the housing and having a sealing cone adapted to close a connection of large throughflow cross-section at the opposite end of the housing which also has a side connection for the supply of pressurized fluid to a working cylinder of a mine-roof support, the large throughflow cross-section at the connection thereby guaranteeing brisk pushing-in of a piston rod of a piston in the cylinder.</p>
