"Vanes, gears, pistons, or diaphragms are used to separate the fluid into known volumes." . "Qualified" . "POSITIVE DISPLACEMENT FLOW METER" . "POSITIVE DISPLACEMENT FLOW METER" . "RDS418094" . "A flow meter that measures the volumetric flow rate of a liquid or gas by separating the flow stream into known volumes and counting them over time." . "u20683" . "2006.06.08" . .