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When we need to install a semi-steel pressure gauge for flow measurement, how do we calculate the flow range to set the semi-steel pressure gauge? Typically, when setting up a semi-steel pressure gauge, we need to determine the variable that the device will measure, such as flow rate, liquid level, volume, mass, etc. Then, we must calculate the flow range of the semi-steel pressure gauge. Below is an explanation of the operating principle, measurement accuracy, types, and structural principles of semi-steel pressure gauges. Operating principle of semi-steel pressure gauges: When a semi-steel pressure gauge is placed in a pipeline containing fluid whose flow rate is to be measured, it causes a pressure drop, and this pressure drop varies with the flow rate. A semi-steel pressure gauge is used to measure this pressure drop, which can be used to calculate the flow rate. Variables in the measurement using semi-steel pressure gauges: It is necessary to understand the details of fluid flow within the pipes and the semi-steel pressure gauge; fluids with a uniform flow cross-section will gather in the holes located upstream of the semi-steel pressure gauge. As the fluid flows out of the opening of the semi-steel pressure gauge, its cross-section is smallest and uniform over a certain distance; thereafter, the cross-section of the fluid begins to expand downstream. Upstream of the orifice, before the fluid converges, the pressure of the fluid (P1) is at its maximum. As the fluid begins to converge, the pressure entering the orifice decreases. When the fluid flows out of the orifice, its pressure is at its lowest value (p2) [www.shhzy3.cn], and this minimum pressure remains constant at the smallest cross-sectional area where the fluid flows downstream. The semi-steel pressure gauge connected between point 1 and point 2 measures the pressure difference between these two points (P1 – P2); this value serves as an indication of the flow rate of the fluid through the pipeline during calibration. Semi-steel pressure gauge types: Like most instruments, the ideal type of semi-steel pressure gauge depends on the application. Semi-steel pressure gauges are manufactured in different forms to meet specific application requirements. The shape, size, and position of the holes on semi-steel pressure gauges define the following types of semi-steel pressure gauges: — Concentric semi-steel pressure gauges — Eccentric semi-steel pressure gauges — Throttled semi-steel pressure gauges — Quadrant-edge semi-steel pressure gauges. Concentric semi-steel pressure gauges are made of stainless steel, with thicknesses ranging from 3.175 millimeters to 12.70 millimeters. Any of the following parameters shall not exceed the plate thickness at the edge of the orifice: —1 – D / 50, where D = inner diameter of the pipe; —2 – d / 8, where d = diameter of the orifice; —3 – (Dd) / 8. Beta ratio (β): it is the ratio of the orifice diameter (d) to the inner diameter of the pipe (D). The eccentric semi-steel pressure gauge is similar to the concentric semi-steel pressure gauge; the only difference is that its offset hole is tangent to the center, aligned with the tube, and has a diameter equal to 98% of the tube’s diameter. It is commonly used to measure media containing solid particles – aqueous oils – wet steam. The throttling semi-steel pressure gauge has a hole in the shape of a semicircle or part of a circle, with a diameter that is usually 98% of the pipe diameter. Quadrant edge semi-steel pressure gauges – This type of semi-steel pressure gauge can be used with fluids such as crude oil, highly viscous syrups, or slurries. This semi-steel pressure gauge can be used when the Reynolds number is 100,000 or higher, or between 3,000 and 5,000, with an accuracy coefficient of approximately 0.5. Advantages of semi-steel pressure gauges: This is a very inexpensive and simple method for measuring flow rate; it features predictable behavior, requires less space, and can be used to measure flow velocities in large pipelines. Limitations of semi-steel pressure gauges: The length of venous constriction depends on the roughness of the inner wall of the pipe and the clarity of the semi-steel pressure gauge. In some cases, due to the factors mentioned above, it is difficult to determine the minimum pressure (P2). The pressure recovery capacity downstream is very poor; in other words, the total loss varies between 40% and 90% of the pressure difference. Upstream, it is necessary to straighten the blades to achieve laminar flow conditions. The suspension gets clogged as it flows, the semi-steel pressure gauge is corroded, and for this reason, errors occur after some time. Moreover, semi-steel pressure gauges have low physical strength and a low discharge coefficient. Shanghai No. 3 Factory of Automatic Instruments: http://www.zdhybsc.cn/ Shanghai No. 4 Factory of Automatic Instruments: http://www.zdhybc.cn/