Two identical oval rotors mesh together by means of slots around the gear perimeter. The oval shaped gears are used to sweep out an exact volume of the liquid passing through the measurement chamber during each rotation. The flow rate can be calculated by measuring the rotation speed. Close tolerances ensure that leakage is minimized. In contrast to nutating disc meters, the calibration factor does not vary with viscosity. Though claims for high performance are made, oval gear flowmeters are generally not as precise as the sliding vane design. Another disadvantage is that pulsations are introduced into the flow by the meter. Oval gear meters are typically used in the measurement of solvents and 'dry' liquids. Maximum viscosity allowed: 1,000 centipoise.

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