Rotary flow meter

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A rotameter, also known as a float meter, is a type of variable-area flowmeter. It consists of a conical tube and a rotor (also called a float) that can move up and down freely inside the conical tube. The rotor flowmeter body can be connected to the measurement pipeline using flanges at both ends, threads, or hoses, and is installed vertically on the measurement pipeline. When the fluid flows into the conical tube from below, it is intercepted by the rotor, thereby creating a pressure difference between the upstream and downstream sides of the rotor. Driven by this pressure difference, the rotor rises. There are three forces acting on the rotor: the dynamic pressure of the fluid on the rotor, the buoyant force exerted by the fluid on the rotor, and the rotor’s own weight. 　　When a rotameter is installed vertically, the center of gravity of the rotor coincides with the axis of the conical tube, and the three forces acting on the rotor are all parallel to the tube axis. When these three forces are in balance, the rotor floats steadily at a certain position within the conical tube. For a given rotameter, the size and shape of the rotor are already determined; therefore, both its buoyancy in the fluid and its own weight are known constants. Only the dynamic pressure exerted by the fluid on the float varies with the flow velocity. Therefore, when the incoming flow velocity increases or decreases, the rotor moves upward or downward, and the flow cross-sectional area at that position also changes, until the velocity reaches the value corresponding to equilibrium; at that point, the rotor stabilizes in its new position. For a given rotameter, the position of the rotor within the cone tube is in a one-to-one correspondence with the flow rate of the fluid passing through the cone tube.