Abstract: Microwave digestion vessel of Teflon PFA material including a Teflon PFA vessel with a threaded top and a Teflon PFA cap with internal threads for engaging the vessel threads. A valve assembly extends upwardly from a center portion of the cap and includes a valve seat, a valve ball internal thereto, a Teflon spring uniquely configured and a valve cap holding the spring and ball into the ball seat of the valve seat. An exhaust hole is provided out one side of the valve cap. The vessel includes a flange for encompassing a lower portion of the cap for pressure expansion protection. A ring with an adjoining flange is also provided for the cap to provide for pressure expansion protection.