A centrifugal processing unit for directing the movement of substances within a sample processing cartridge, the centrifugal processing unit comprising: at least one rotor with at least one accommodation for receiving the sample processing cartridge, the at least one accommodation only allowing a free pivoting motion of the cartridge about a respective pivot axis, wherein each pivot axis is orthogonal to a rotor axis of the at least one rotor and to a respective force vector (F1, F2, F3) of a centrifugal force, at least one rotor drive for rotating the at least one rotor about the respective rotor axis to create the centrifugal force, a control for accelerating and decelerating the at least one rotor, at least one blocking element, allowing the free pivoting motion of the cartridge in a release position and preventing the free pivoting motion in a blocking position, wherein the blocking element can be moved into the release position when the rotor is rotated in a first direction of rotation and wherein the blocking element can be moved into the blocking position when the rotor is rotated in a second direction of rotation, opposite to the first direction of rotation, characterized in that each accommodation is allocated on a free end of a rotor arm, wherein the blocking element comprises a disk with arms with blockers and with stoppers (343,344), wherein the disk is fixed to the rotor shaft, wherein the arms extend laterally outward from the disk in a substantially radial direction, on opposite sides of the disk, wherein at the free end of each arm, one blocker is arranged and designed to engage with a respective protrusion of the at least one accommodation, wherein the stoppers (343,344) extend from the disk in the direction of the rotor axis and are designed to abut the respective rotor arm sideways. at least one rotor with at least one accommodation for receiving the sample processing cartridge, the at least one accommodation only allowing a free pivoting motion of the cartridge about a respective pivot axis, wherein each pivot axis is orthogonal to a rotor axis of the at least one rotor and to a respective force vector (F1, F2, F3) of a centrifugal force, at least one rotor drive for rotating the at least one rotor about the respective rotor axis to create the centrifugal force, a control for accelerating and decelerating the at least one rotor, at least one blocking element, allowing the free pivoting motion of the cartridge in a release position and preventing the free pivoting motion in a blocking position, wherein the blocking element can be moved into the release position when the rotor is rotated in a first direction of rotation and wherein the blocking element can be moved into the blocking position when the rotor is rotated in a second direction of rotation, opposite to the first direction of rotation, characterized in that each accommodation is allocated on a free end of a rotor arm, wherein the blocking element comprises a disk with arms with blockers and with stoppers (343,344), wherein the disk is fixed to the rotor shaft, wherein the arms extend laterally outward from the disk in a substantially radial direction, on opposite sides of the disk, wherein at the free end of each arm, one blocker is arranged and designed to engage with a respective protrusion of the at least one accommodation, wherein the stoppers (343,344) extend from the disk in the direction of the rotor axis and are designed to abut the respective rotor arm sideways.