Elliptical gear flow meters , also known as displacement flow meters, are a type of volumetric flow meter. They are among the most accurate flow meters and are suitable for measuring the flow of high-viscosity media, but not for fluids containing solid particles. They mainly consist of a metering chamber, a sealing mechanism, and a counting mechanism.
1. Measuring Chamber: The instrument housing ① (as shown in the figure) is made of cast iron, and its inner cavity and cover plate ④ form the measuring chamber. Inside the measuring chamber are two stainless steel shafts ②, on which a pair of oval gears ③ are mounted. Driven by the pressure difference between the inlet and outlet of the flowmeter, they rotate, continuously conveying the liquid from the inlet through the crescent-shaped cavity to the outlet. Each rotation accumulates to a volume four times that of the crescent-shaped space. The gap between the oval gears and the inner wall of the measuring chamber is very small, only tens of micrometers, to reduce instrument leakage.
2. Sealing Mechanism: The measuring chamber of the instrument is sealed. Small-diameter flow meters employ a permanent magnetic sealing mechanism (as shown in the figure): the active permanent magnet ⑥ and the passive permanent magnet ⑦ are separated by a partition ⑧. This structure offers high sensitivity and reliable sealing. Large-diameter flow meters use polytetrafluoroethylene (PTFE) plastic as the packing seal (as shown in the figure): the compression of the spring ⑦ is changed by adjusting the nut ③, causing the sealing gasket ⑥ to expand and achieve a seal. This structure is relatively simple and easy to adjust.
3. Counting Mechanism: The counting mechanism of the instrument includes a traditional gear train, a transmission ratio adjustment mechanism, and a settlement mechanism. The total number of rotations of a pair of elliptical gears and their speed are transmitted to the pointer and dial wheel of the settlement mechanism (11) after being changed by the transmission gear train (10), so that the total amount of liquid and instantaneous flow rate in the pipeline can be known. The transmission ratio adjustment mechanism is used to adjust and correct the instrument error. The elliptical gear flow meter has an electric pulse transmitter installed in the elliptical gear flow counting mechanism. That is, a disc with a permanent magnet is installed on the transmission shaft at the sealed part of the elliptical gear flow meter, and a new type of magnetically sensitive integrated sensor is installed on the counter. This sensor has the advantages of long life, strong anti-interference ability, wide operating frequency, no spark, no fear of oil and dust, small size, and convenient installation. When the magnet approaches its sensing surface and reaches the action distance, a reliable detection signal can be generated without contact.
