Dual-rotor flow meter

The twin-rotor (screw) flowmeter is a uniquely designed positive displacement flowmeter primarily used for measuring liquid flow rates. Its measuring unit consists of two spiral rotors, whose interaction is controlled by a set of precise gears, as shown in Figure 4-5. Structurally, it can also be divided into two types: the standard double-rotor type and the axial-flow double-rotor type, as shown in Figures 4-5a and b respectively. The measurement principle of the twin-rotor flow meter is the same as that of the various rotor-type flow meters mentioned above; the number of rotations of the meter’s rotors is directly proportional to the total volume of fluid passing through it. Therefore, by transmitting the number of rotations of the rotors to a counting and indicating mechanism through a gear system, it is possible to determine the flow rate. In addition to having a direct-reading counter for local indication of flow rate, the twin-rotor flow meter can also be equipped with a pulse generator that converts the number of rotations of the rotors, which is proportional to the volumetric flow rate passing through the meter, into pulse signals. This allows easy connection to a flow integrator or a computer. The structure of the screw flow meter is somewhat similar to that of the axial-flow twin-rotor type, as shown in Figure 4-5c. That is why screw flow meters are also referred to as twin-rotor flow meters.