What is the difference between an elliptical gear flow meter and a Roots flow meter?

The oval gear flow meter (also known as a displacement flow meter or gear flow meter) belongs to the category of positive-displacement flow meters, and it is one of the types with high accuracy among flow measurement instruments. It uses mechanical measuring elements to continuously divide the fluid into individual, known volume portions, and measures the total volume flow rate based on the number of times each such volume portion is filled and emptied in the metering chamber. An elliptical gear flowmeter consists of a metering box and a pair of elliptical gears installed within it; together with the upper and lower cover plates, they form a sealed crescent-shaped cavity (which is not completely sealed due to the rotation of the gears) that serves as the unit for calculating the volume per discharge. When the liquid to be measured enters the flow meter through a pipe, the pressure difference created at the inlet and outlet drives a pair of gears to rotate continuously, thereby transporting the liquid that has been measured in the initial crescent-shaped chamber to the outlet. The total flow rate of the liquid being measured is equal to the product of the number of rotations of the elliptical gears and four times the volume discharged with each rotation. A flow meter mainly consists of a housing, a counter, elliptical gears, and couplings (including magnetic couplings and axial couplings). A Roots flow meter, also known as a gear flow meter, is a high-precision measuring instrument primarily used for the continuous or intermittent measurement of the flow rate of gases or liquids in pipelines. It features high precision, good reliability, light weight, long service life, low operating noise, and ease of installation and use. The gear flow meter can display cumulative flow, instantaneous flow, and single measurement values on-site; it can also output pulse signals, 4-20mA or 1-5V analog signals, as well as support 485 communication, 4-20mA+HART, and MODBUS protocols. A gear flow meter consists of a metering chamber, a metering rotor, a metering component assembly (i.e., the internal measuring elements), and a counting indication assembly. Inside the housing of the gear flow meter, there is a metering chamber. Within this chamber, there is one or two pairs of gears that can rotate in tangential fashion (in fact, they are gears with a module of 2). Outside the flow meter’s housing, along the same axis as these gears, there is a pair of drive gears; these gears mesh with each other, enabling the two gear sets to move in unison. Working principle: The Rotameter uses mechanical measuring elements to continuously divide the fluid into individual, known volume portions, and measures the total volume flow rate by counting the number of times each such volume portion is filled and emptied in the metering chamber. When the fluid under test flows through the flow meter, its dynamic pressure creates a pressure difference between the inlet and outlet, which drives the gear wheels to rotate. As the fluid causes the gear wheel on shaft D2 to rotate counterclockwise, as shown in Figure 1A, the connected drive gear causes the gear wheel on shaft D1 to rotate clockwise; after rotating 90 degrees, it reaches the state shown in Figure 1C. The upper gear wheel rotates clockwise due to the influence of the fluid, while the drive gear causes the lower gear wheel to rotate counterclockwise. When the gear wheels have rotated 360 degrees, four times the effective volume of the measurement chamber’s volume of fluid is discharged from the flow meter. In this way, the two idler wheels drive rotation in turn; as the idler wheels rotate, the fluid is continuously discharged from the flow meter through the metering chamber. The volume of fluid discharged per rotation of the gear pump is a constant value; in other words, the discharge volume is proportional to the number of rotations of the gear pump shaft. Through the gear pump shaft and other transmission mechanisms, the rotation speed is reduced before the signal is transmitted to the cumulative display unit. It is precisely this working principle of the vane flow meter that ensures high accuracy and a low starting flow rate, as long as the clearance design inside the measuring chamber and the assembly are proper. This characteristic is extremely important for gas metering in residential areas; it not only meets the accuracy requirements for normal gas usage by residents but also overcomes the limitation of other types of flow meters to measure small amounts of gas used during off-peak times.

The gear flow meter, also known as the elliptical gear flow meter, belongs to the category of positive displacement flow meters. It is mainly used for measuring the flow rate of media with high viscosity. A Roots flow meter is somewhat similar to a gear, but its tooth shape is special – it usually has two or three teeth with large spaces between them. It is generally used for measuring low-viscosity fluids, and can even be used with gases.