Abstract: A hydraulic dual-circuit external power brake valve of tandem design has a primary control piston and a secondary control piston, both of which are located in a valve bore of the dual-circuit external power brake valve. The control pistons are provided with bores for connection of a primary brake circuit and a secondary brake circuit to a pressure reservoir and an equalizing tank, and are movable within the valve bore. The regulating force necessary for the motion is introduced into the dual-circuit external power brake valve by a regulating spring. A pressure-transmitting piston between the primary control piston and the regulating spring. The primary control piston on its two end faces, and the pressure-transmitting piston on its face toward the primary piston, are subjected to the pressure acting in the primary brake circuit. When the primary brake circuit is intact, the pressure-transmitting piston is actuated by the regulating spring.