Abstract: The control device is applicable as a hydraulic regulating valve for controlling a power lift unit of a tractor and comprises a mechanically actuated preliminary selector valve operable for reciprocal movement to close or open pressure fluid supply into a control chamber counteracting a reciprocal main pressure control valve that is spring loaded against the control chamber. To avoid permanent choking resulting from pressure changes due to the movement of the control edges, a section of the preliminary control slide is recessed to such an extent as to exert elastic extension when subject to increased pressure, the extension being within the limits of elasticity of the material of the slide.

Abstract: A main valve has a housing, a valve member slidable in the housing and defining at its opposite ends two pressure chambers, a high-pressure port and a low-pressure port of which one communicates with one of the chambers, a throttle connecting the chambers and a spring acting in the other chamber upon one end of the valve member and urging the same from a blocking position towards a rest position. A control valve has a fluid line which communicates with the other of the chambers for selecting a main-valve response pressure. A first set of passages connects the ports with one another via the one chamber when the valve member approaches the rest position thereof, and a second set of passages connects the chambers with one another when the valve member approaches its blocking position.