Digraph Embedding on T h .

A variable sweep means connects the rotating shaft of an electric motor to a rotatable gas manifold in a rotary disc reactor to convert rotation of the shaft into reciprocating oscillation of the gas manifold. A cycle timing control means for varying electric motor speed at two independent speeds is connected to the electric motor. The control means varies the oscillation speed of the gas manifold at two sweep rates by varying electric motor speed automatically during each sweep cycle.