[en] A pump was required for metering concentrated neutralized high-level liquid wastes mixed with glass formers to an electric melter for the nuclear waste vitrification process. An air-displacement slurry pump with a pneumatic actuated 2-way valve and microprocessor controller was found to best satisfy the requirements developed at the Pacific Northwest Laboratory (PNL). A 2-stage air lift was successfully used to meter slurries of acidic waste mixed with glass formers. Five candidate pumps were chosen for testing after an extensive review of commercially available pumps, present industrial practices, and the literature. Test procedures and results are described. 6 references, 4 figures