An erector for holding a leaf-flap in various opening settings

An erector for holding a leaf-flap in various opening settings relative to its frame, having a continuously length-variable dynamic unit 1, which comprises a hollow cylinder 2 and a piston 3 which is slidably guided in the hollow cylinder 2 by a piston rod 4 to divide the hollow-cylinder space into two pressure-medium chambers 7, 8 which are in fluid communication through a flow regulator 5. In order to enable the restraining forces of the erector when the leaf-flap is moved to be substantially reduced in one directional sense, there is disposed in one of two overflow ducts 11, 12 of the flow regulator 5 a control valve 14, by which the assigned overflow duct 12, when the control valve 14 is closed, is flow-blocked in both directions, the control valve being constantly in fluid communication via a control duct 18 to one of the pressure-medium chambers. The control valve 14, as it is acted upon by the pressure-medium column flowing through the control duct, is transferred against a return force into a pass-through setting in which it is maintained up to a pressure level of the pressure medium which is significantly lower than the control pressure of the control valve 14.