The Basic Principle and Construction of Elastic Scraper Flow Meters

　　The Basic Principle and Construction of Elastic Scraper Flow Meters

　　Principle

　　When the liquid to be measured is injected into the flowmeter through its channel, a pressure difference develops between the inlet and outlet of the flowmeter. This pressure differential drives the rotation of the scraper blades and the rotor. Inside the flowmeter housing, the measuring chamber—formed by the inner wall of the casing, the motor rotor, and the outer centerlines of the two scraper blades—is completely filled with the liquid under test. As the motor rotor spins in the direction indicated by the arrow, the three scraper blades sequentially create individual measuring chambers, which then continuously push the liquid from the inlet side toward the outlet side. With each full rotation of the motor rotor, exactly three fixed-volume increments of liquid are discharged. Therefore, by simply measuring the rotational speed of the motor rotor, it becomes possible to determine the total volume of liquid flowing through the flowmeter. Finally, the rotational motion of the stator is transmitted via a magnetic coupling assembly to the gear-driven adjustment mechanism, which converts the number of rotor rotations into corresponding volumetric flow values on the platform display. These values are either accumulated and displayed by an electronic counter or converted into electronic signals via a transmitter, enabling precise measurement and monitoring throughout the entire process.

　　Construction

　　It consists of three main components: a flow meter for precise measurement of the moving entity, a counting display mechanism, and a transmitter.

　　The precision measuring mechanism primarily consists of a housing, stop blocks, shims, a motor rotor, scrapers, a torsion spring, a central shaft, upper and lower bearing end caps, and a flange plate. The three scrapers are individually packaged on the motor rotor, with their rotating radius designed to expand and contract continuously while maintaining constant contact with the inner wall of the housing. Thanks to the stop blocks, the scraper’s rotating radius can be reduced as needed. To enhance durability and performance, a specially engineered layer of acid- and alkali-resistant, highly wear-resistant, and elastic plastic is applied over both the scrapers and the rotor. Additionally, the shims are crafted entirely from this same robust plastic material. Meanwhile, the motor shaft’s output end features a hermetically sealed connection to ensure optimal functionality. By implementing these advanced design features—combined with the inherent elasticity provided by the torsion spring integrated into the scrapers—the precision measuring unit achieves a smooth, gentle interaction between its stationary and moving components. This innovative approach not only eliminates unwanted side and axial clearances, thereby preventing leakage, but also safeguards against clogging, damage, or failure caused by residual debris, solid particles, or even liquid contaminants. As a result, the elastic scraper flowmeter delivers unparalleled accuracy in measurement, ensuring reliable and consistent performance under diverse operating conditions.

　　The counting mechanism consists of a transmission gear adjustment assembly, an electronic counter, and a pointer indicator. The primary function of the transmission gear adjustment assembly is to fine-tune instrument errors, ensuring that the meter reading closely matches the actual value—thus achieving the required measurement accuracy. Typically, deviations in the meter’s display accuracy are caused by component size inaccuracies or improper installation. Therefore, before the flow data is accumulated by the electronic counter, adjustments must first be made by the dedicated calibration department. The transmission gear adjustment assembly achieves error correction by altering the gear ratio of the transmission mechanism through the use of interchangeable gears. Meanwhile, the electronic counter accumulates the total flow volume, while the indicator displays the instantaneous flow rate at any given moment.

　　The transmitter converts the angular velocity of the flowmeter input shaft into a pulse current signal corresponding to the total flow rate, transmitting it over long distances to various flow totalizers for displaying either the total fluid volume or the instantaneous flow rate—and also sending it remotely to control systems.

　　To accommodate different applications, the elastic scraper flowmeter is available in two versions: a general-purpose model and a corrosion-resistant model. For the general-purpose version, components that come into direct contact with the process medium are made from materials such as cast steel, stainless steel, leaded brass, and nitrile rubber. This version is suitable for operating temperatures below 80°C and works well with non-corrosive media, such as various types of refined oils. In contrast, the corrosion-resistant model features all metal parts that directly interact with the medium crafted from high-grade stainless steel IGr18NDTi, while the sealing elements are made from fluorocarbon rubber.