Concave adjustment system in a combine harvester twin axial-flow crop processor

A combine harvester comprising:

• a frame;
• two axial-flow crop processing rotors mounted to the frame and arranged side-by-side, each rotor having a longitudinal rotation axis;
• an inner support structure located between, and extending parallel to, the two rotors, the inner support structure movably suspended from the frame by a first linkage;
• two outer support structures located outboard of, and extending parallel to, the two rotors, the outer support structures movably suspended from the frame by respective second and third linkages;
• wherein the inner support structure and the two outer support structures are configured to carry first and second pluralities of concave grate segments at a radial distance from the respective rotors;
• and,
• a concave adjustment system comprising:
• a first hydraulic actuator coupled to the first linkage and configured to raise and lower the inner support structure;
• a second hydraulic actuator coupled to one of the second and third linkages and configured to raise and lower at least one of the two outer support structures;
• and
• a hydraulic control system comprising:
• the first and second hydraulic actuators;
• and
• first and second pressure relief valves, each valve hydraulically connected to a respective one of the first and second hydraulic actuators, wherein the first and second pressure relief valves permit movement of the inboard and outboard sides of the concave gate segments respectively in response to slugs of crop material passing adjacent the concave grate segments.