Abstract: Anti-leak two-port and three-port poppet valves for a regenerative thermal oxidizer in which a gas such as contaminated air is first passed through a hot heat-exchange bed and into a communicating high temperature oxidation (combustion) chamber or zone, and then through a relatively cool second heat exchange bed. The alternating of the heat transfer zones to provide matrix regeneration is accomplished via regenerative thermal oxidizer switching valves. In the preferred embodiment of the present invention, the switching valves are horizontal pneumatic poppet type valves in a consolidated housing, the valve's switching frequency or cycle being a function of volumetric flow rate.