The invention comprises a roof supporting system for use in a mine working employing a row of roof supports each having an inner unit and an outer unit incorporating hydraulic props and advanced in turn by hydraulic ram means. A control valve provided on each of the supports can be moved into a position to depressurize the props of the inner unit of that support to pressurize the props of an outer unit on an adjacent one of the supports in the system and advance these two units simultaneously so that each support need be visited only once by an operator to bring about advancement of all the units in the whole supporting system. Each control valve may have selectively usable outlets to enable the outer unit of an adjacent support on one side or the other of that incorporating the control valve to be advanced simultaneously with the inner unit of the latter support.
