The present invention relates to a downhole tool, comprising a hydraulic assembly, an arm assembly, the arm assembly comprising a wheel, a hydraulic motor for rotating the wheel, thereby driving the downhole tool in a forward direction, and a hydraulic pump unit for simultaneous generation of a first and a second pressurized fluid, characterized in that the arm assembly is movable between a retracted position and a projecting position in relation to the tool housing, and the downhole tool furthermore comprises an arm activation assembly for moving the arm assembly between the retracted position and the projecting position, and the hydraulic motor drives the downhole tool in the forward direction when the arm assembly is in the projecting position, the arm activation assembly being in fluid connection with the first pressurized fluid and the hydraulic motor being in fluid connection with the second pressurized fluid, a hydraulic control block for controlling the pressure of the first pressurized fluid having a first pressure and controlling a second pressure of the second pressurized fluid, and a hydraulic control block comprising a first sequential valve for controlling a sequence of retraction of the arm assembly, a projection of the arm assembly and a rotation of the wheel, wherein the sequential valve is fluidly connected with one of the fluids and changes between an open and a closed position based upon the pressure of the other fluid. Furthermore, the present invention relates to a method of controlling a projection of an arm assembly of a driving unit of a downhole tool and to a downhole system.