Flow meters with improved blocking and displacement rotors

A flow meter (10) with a metallic case (11) and bearing plates (61) but with a blocking rotor (15) and displacement rotors (16) that are polymeric is provided. The rotors (15) may be sized for a reduced clearance between the rotors (15) and surfaces (28) of the case (11), bearing plates (61) and blocking rotor (15). Using closer clearances between the rotors (15) and the case (11)/bearing plates (61) reduces leakage and provides for a more accurate measurement of the fluid through the flow meter (10). 种具有金属外壳(11)和支撑板(61)但具有由聚合物制成的阻挡转子(15)和位移转子(16)的流量计(10)。转子(15)的尺寸可以适合于转子(15)与外壳(11)的表面(28)、支撑板(61)和阻挡转子(15)之间的减小间隙。在转子(15)与外壳(11)/支撑板(61)之间使用更紧密的间隙减小了泄漏并且允许更准确地测量通过流量计(10)的流体。