# Level and Flow Measurement

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# Working Principle Of Metal Tube Float Flowmeter

##### Author:vacorda    Source:www.vacorda.com    Date: 2020-07-13 11:40:18

The rotameter consists of two parts. One of the rotameter is a tapered tube that gradually expands from bottom to top; the other is a rotor that is placed in a tapered tube and can move freely up and down along the center line of the tube . Rotor flowmeter When measuring the flow of fluid, the measured fluid flows in from the lower end of the conical tube. The flow of the fluid impacts the rotor and generates a force on it (this force changes with the flow); when the flow is large enough When the force is generated, the rotor is lifted and raised. At the same time, the measured fluid flows through the annular cross-section between the rotor and the tapered tube wall. At this time, there are three forces acting on the rotor: the dynamic pressure of the fluid on the rotor, the buoyancy of the rotor in the fluid, and the gravity of the rotor itself. When the flowmeter is installed vertically, the center of gravity of the rotor will coincide with the tube axis of the cone tube, and the three forces acting on the rotor are in the direction parallel to the tube axis. When these three forces reach equilibrium, the rotor floats smoothly at a certain position in the cone tube. For a given rotameter, the size and shape of the rotor have been determined, so its buoyancy in the fluid and its own gravity are known to be constant, only the dynamic pressure of the fluid on the float changes with the size of the incoming flow velocity . Therefore, when the incoming flow velocity becomes larger or smaller, the rotor will move up or down, and the flow cross-sectional area at the corresponding position will also change. Until the flow velocity becomes balanced at the corresponding speed, the rotor will stabilize at the new position. For a given rotameter, the position of the rotor in the cone tube has a one-to-one correspondence with the amount of fluid flowing through the cone tube.

In order to prevent the rotor from touching the wall when moving up and down the center line of the tapered tube, two methods are usually used: one is to install a guide mandrel in the center of the rotor to keep the rotor on the center line of the tapered tube. Moving up and down, the other is that there is a chute on the edge of the rotor disc. When the fluid flows through the rotor from bottom to top, it will bypass the rotor on the one side and generate a reverse thrust through the chute at the same time, so that the rotor will not rotate around the centerline. When it stops rotating, it can keep the rotor from hitting the tube wall during working. The rotor material of the rotameter can be made of stainless steel, aluminum, bronze, etc.

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