Abstract: An inventive cam actuation structure provides a separate cam member for opening each of the valves in a regenerative thermal oxidizer. The separate cam structures allow the arrangement of the flow passages in any desired relationship relative to the other passages. In addition, the use of the separate cams allows great variability in the adjustment of the valve profiles relative to each other. Two valve actuation structure embodiments are disclosed. In a second feature of this invention, the inlet manifold is received within the outlet manifold. The heated gas in the outlet manifold preheats the gas in the inlet manifold, ensuring that impurities will not liquify within the inlet manifold. In a further feature of this invention, gravitational controls are used for the purge valve. A connection between the inlet valve and the weights for opening the purge valve ensures that the purge valve will not be opened when the inlet valve is opened.