The circular gear flowmeter is a positive displacement flow transmitter used to measure volume flow with high accuracy. With the flow of the medium, the gear meshes and rotates, under the action of fluid flow, the pressure difference is formed at both ends of the import and export of the instrument, no power supply is required, and a pair of gears rotate freely, the cavity between the gears is filled with liquid, the liquid is discharged with rotation, the number of revolutions of the gear can be measured to know the flow rate of the liquid.