Abstract: A valve seat and a valve assembly incorporating such valve seat form tight dual seals with glass lined nozzle of a reagent or reaction vessel. This reduces or eliminates cavities and crevices between the value seat and the nozzle where residues or contaminants can accumulate. Additionally, the present valve assembly comprises flush ports to permit the valve seat and the valve to be cleaned-in-place. This eliminates the need to disassemble the valve seat and/or the valve to remove the contaminants, thereby minimizing process “down time.