A processing installation for devolatilization of polymer melts comprises a first extruder and a second extruder arranged downstream thereof in a direction of conveyance. The first extruder comprises several rotatably drivable first shafts which are provided with first treatment members and several devolatilization zones with associated devolatilization ports. Correspondingly, the second extruder comprises several rotatably drivable second shafts which are provided with second treatment members and several second devolatilization zones with associated devolatilization ports. The first treatment members have an external diameter which is smaller than or equal to that of the second treatment members. A devolatilization unit is arranged in a transfer zone which interconnects the extruders. The devolatilization unit comprises a perforated plate and a clearance arranged downstream in the direction of conveyance. A control unit is configured in such a way that when the processing installation is operated, the speed of the second shafts is lower than the speed of the first shafts. The processing installation allows a high devolatilization performance and a high polymer throughput to be achieved at the same time. A throttle is arranged in the transfer zone upstream of the devolatilization unit when seen in the direction of conveyance, with the position of the throttle being adjustable by means of the control unit.