What is a twin-rotor Roots flow meter?

Roots blowers are at least double-rotor, and there are also triple-rotor ones. The volume of material transported remains the same for each rotation of the Roots rotor; it is this volume that is measured based on the number of rotations.

It is a Roots flow meter with two rotors. Working principle: A pair of helical rotors with special tooth profiles in the flow meter mesh directly with each other, without any relative sliding, and no synchronous gears are required. The rotor rotates driven by a small pressure difference at the inlet and outlet. At the same moment, although the rotational torque exerted by the fluid on each rotor at the same cross-section is different, the total rotational torque exerted on the two rotors at all cross-sections is equal. Therefore, the two rotors rotate at a constant speed and with a constant torque each, resulting in balanced displacement without pulsation. Each rotation of the helical rotor generates a volume equal to 8 times that of the cavity; therefore, the number of rotations of the rotor is proportional to the cumulative flow rate of the fluid, while the rotational speed of the rotor is proportional to the instantaneous flow rate of the fluid. The rotation speed of the rotor is transmitted to the gauge counter via a magnetic coupling, thereby indicating the flow rate passing through the flow meter (through the pipeline).