Abstract: An ovalizer which employs hydraulic cylinders to directly actuate duct forming members for forming round spiral duct to oval. The ovalizer includes a pair of elongated and laterally spaced-apart duct forming members sized to fit within a ductwork section and to bear against opposing interior surfaces of the ductwork section. Spaced longitudinally along and between the duct forming members are a plurality, five in the disclosed embodiment, of double-acting hydraulic cylinder assemblies for selectively forcing the duct forming members apart for forming round duct to oval, and retracting the duct forming members towards each other at the conclusion of a forming operation. A feedback control system ensures that the hydraulic cylinder assemblies extend together at approximately the same rate and stop when a predetermined extended position is reached.