Two chamber regenerative thermal or catalytic oxidizer with purging circuit

A two chamber regenerative thermal oxidizer comprises an oxidizing chamber and a pair of regenerator chambers. Inlet and outlet valves control fluid flow to and from said regenerator chambers. A transition duct communicates with a contaminated fluid feed duct upstream of the regenerator inlet valves and with the oxidizing chamber of said oxidizer. A purge air duct directs the output of the regenerator chambers back to the chambers, selectively. Electronic control means effects powered actuation of said valves, selectively, in a prearranged sequence whereby the inlet and outlet valves in the respective regenerators are never open at the same time thereby precluding short circuiting of the regenerative chamber, yet all of the inlet and outlet valves to the regenerative chambers are never simultaneously closed thereby to maintain the pressure of fluid flow through said regenerator chambers relatively constant.