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I. Types and Characteristics of Insertion Flow Meters 1. Types Flow meters are generally classified based on their principle of operation, such as throttle, vortex street, electromagnetic, ultrasonic, etc. Most of these meters are installed on pipelines using flanges. As the name implies, an insert-type flow meter is a flow measuring instrument that is installed by being inserted into the pipeline, and it calculates the flow rate by measuring the flow velocity at one (or several) points within the pipeline. It can be said that any instrument capable of measuring flow velocity can function as an insert-type flow meter (this article focuses only on insert-type flow meters used to measure flow velocity at a single point). Commonly used types of such flow meters include: (1) the pitot tube, which is a classic and relatively accurate flow meter that was widely used for on-site measurements decades ago. Due to the risk of clogging and low differential pressure output, it is now rarely used in industrial settings, but it is still often used for calibration purposes. (2) The Pitot-Venturi tube, also known as a dual trumpet tube or dual Venturi tube, is based on the principle of speed measurement using a pitot tube. It features design elements that facilitate acceleration and pressure reduction; under the same flow conditions, it can generate a greater pressure difference compared to a typical pitot tube. It is less prone to clogging and can withstand high temperatures, but its accuracy is not high. (3) Other flow meters such as vortex flow meters, turbine flow meters, and electromagnetic flow meters can also indicate the magnitude of the flow velocity. It can be turned into a compact measuring probe, which uses the measurement of flow velocity at a certain point in the pipeline to determine the flow rate. 2. Advantages and disadvantages: (1) Simple structure, lightweight, and low manufacturing cost. (2) It has low pressure loss and low operating costs, making it an energy-saving instrument. (3) One structure can be used for multiple calibers (limited to point-speed type), reducing the number of spare units required by users. (4) Easy to package, transport, install, and maintain. (5) Installation and removal can be carried out without interrupting the flow, avoiding economic losses caused by such interruptions. (6) The flow velocity distribution in the pipeline has a significant impact on measurement accuracy, requiring straight pipe sections with a length of 30D to 50D. (7) The on-site conditions are complex, which has a significant impact on its application and makes standardization difficult. (8) It is difficult to improve accuracy; generally, it can only reach ±(3~5%).