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Introduction to the detailed parameters of the float flowmeter

The float flowmeter is a volume flow meter that is measured by a float in a vertical conical tube as the flow rate changes, changing the flow area between them, and is also called a rotameter. In the United States and Japan, it is often called a variable area flow meter (Variable Area Flowmeter) or an area flow meter. The principle of the float flowmeter was conceived in the 1860s, and 20 actual products appeared. In terms of the proportion of application desk trees, the floating flowmeters in 17,000 flow meters of 72 companies in the UK sample survey in 1985 accounted for 19.2%. The output of China's float flowmeter is estimated to be between 150,000 and 170,000 units in 1996, of which about 95% is a glass tube float flowmeter.

Principle and structure of the float flowmeter

The flow detecting element of the float flowmeter is composed of a vertical conical tube which is enlarged from the bottom to the top and a float group which moves up and down along the axis of the conical tube. The working principle is shown in Fig. 1. When the measured fluid passes from the bottom to the annulus 3 formed by the cone 1 and the float 2, a differential pressure is generated at the upper and lower ends of the float to form a lifting force of the float, and the rising force of the float is greater than that of the immersion fluid. When the weight of the float is increased, the float rises, the annulus area increases, the fluid flow rate at the annulus decreases immediately, the differential pressure at the upper and lower ends of the float decreases, and the lifting force acting on the float decreases, until the rising force is equal to the immersion in the fluid. When the weight of the float is reached, the float is stabilized at a certain height. The height of the float in the cone tube corresponds to the flow rate passed.

The basic equation of volume flow Q is

When the float is a non-solid hollow structure (loading adjustment)

Α——the flow coefficient of the meter, which varies depending on the shape of the float;

Ε——the coefficient of gas expansion when the measured fluid is a gas, usually ignored due to the small amount of correction of the coefficient, and it has been included in the flow coefficient by calibration, such as ε=1 for liquid;

△F——circulation ring area, m2;

G——local gravitational acceleration, m/s2;

Vf - float volume, if extended, should also include, m3;

Ρf——float material density, kg/m3;

Ρ——the density of the measured fluid, such as the density of the gas in the cross section upstream of the float, kg/m3;

Ff——the cross-sectional area at the working diameter (maximum diameter) of the float, m2;

Gf - float quality, kg.

The relationship between the circulation annular area and the height of the float. When the structural design has been determined, d and β are constant. In the formula, there is a quadratic term of h. Generally, this nonlinear relationship cannot be ignored. Only when the cone angle is small, it can be regarded as approximate linear.

D——the maximum diameter of the float (ie the working diameter), m;

H——the height of the float from the inner diameter of the cone is equal to the maximum diameter of the float, m;

Β—the cone angle of the cone tube;

a, b - constant.

The typical structure of a 15-40mm transparent tapered tube float flowmeter is shown in Figure 2. The transparent conical tube 4 is most commonly used by borosilicate glass, and is accustomed to the glass tube float flowmeter. The flow indexing is directly engraved on the outer wall of the cone tube 4, and an indexing scale is additionally installed beside the cone tube. The inner cavity of the cone has a smooth surface of the cone and a guiding rib (or plane). The float moves freely within the cone tube, or moves under the guidance of the ribs of the cone tube, and the instrument for guiding the inner wall of the larger smooth surface is guided by a guide rod.

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