Principle of Metal Float Flow Meter | Working Principle of Metal Tube Float Flow Meter

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1. Structural principle of metal float flowmeter

The flow detection element of metal float flowmeter is composed of a vertical conical tube that expands from bottom to top and a float group that moves up and down along the axis of the conical tube. The working principle is shown in Figure 1. When the measured fluid passes through the annular gap 3 formed by the conical tube 1 and the float 2 from bottom to top, a differential pressure is generated at the upper and lower ends of the float, forming a force for the float to rise. When the upward lift force on the float is greater than the weight of the float immersed in the fluid, the float rises, and the annular gap area increases accordingly. The fluid flow velocity at the annular gap immediately decreases, and the differential pressure between the upper and lower ends of the float decreases. The upward force acting on the float also decreases until the upward lift force is equal to the weight of the float immersed in the fluid, and the float stabilizes at a certain height. There is a corresponding relationship between the height of the float in the conical tube and the flow rate it passes through. The basic equation for volumetric flow rate Q is (1) when the float is a non solid hollow structure (load adjustment amount), then in equation (2), α - the flow coefficient of the instrument varies depending on the shape of the float; ε - the coefficient of gas expansion when the measured fluid is a gas, which is usually ignored due to its small correction amount and has been included in the flow coefficient through verification. If it is a liquid, ε=1; △ F - circulating annular area, m2; g - local gravitational acceleration, m/s2； Vf - Float volume, including any ex

(3). When the structural design is determined, d and β are constants. There is a quadratic term for h in the equation, and this nonlinear relationship cannot be ignored. It can only be considered approximately linear when the cone angle is very small. In equation m2 (3), d represents the maximum diameter (i.e. working diameter) of the float, m; h represents the height at which the float rises from the point where the inner diameter of the cone tube is equal to the maximum diameter of the float, m; β represents the cone angle of the cone tube; a. B - Constant. The typical structure of a transparent conical tube float flowmeter with a diameter of 15-40mm is shown in Figure 2. The most commonly used transparent conical tube 4 is made of borosilicate glass, commonly referred to as a glass tube float flowmeter. The flow index is directly engraved on the outer wall of cone tube 4, and there are also additional index scales installed next to the cone tube. The inner cavity of the cone tube has two types: a smooth conical surface and a guide rib (or plane). The float can move freely inside the cone tube or move under the guidance of the cone tube ribs. For instruments with larger smooth inner walls, guide rods are also used for guidance. Figure 3 shows a typical structure of a metal tube float flowmeter with a right angle installation

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