A combine harvester has a crop processing rotor and a concave assembly having at least one concave extending at least partially beneath the rotor in a circumferential manner. The concave assembly is pivotable about pivot point to move the concave in a generally concentric manner toward and away from rotor. An operating mechanism pivots the concave assembly to adjust the operating clearance between the concave assembly and the rotor. The operating mechanism includes an actuator and a linkage assembly connecting the actuator to the concave assembly. The linkage assembly includes a hydraulic cylinder that applies a substantially constant force to the concave assembly to control the pressure put on the crop while the rotor is rotating. A hydraulic supply ports hydraulic fluid to the hydraulic cylinder. The combine harvester also has an accumulator located between the hydraulic supply and the hydraulic cylinder.
