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A differential pressure transmitter, a three-valve assembly, and a throttling device are used together to form a differential pressure flow meter. Common differential pressure flow meters include orifice plate flow meters, V-cone flow meters, wedge flow meters, etc. When using them, it is necessary to strictly follow the operational procedures to prevent damage to the differential pressure transmitter. The structural components of a differential pressure flow meter include a throttling device with two small holes, each of which is connected to a pressure sensing tube. Needle valves are installed on these pressure sensing tubes to regulate the pressure level. Next, there is a three-valve assembly along with a differential pressure transmitter; generally, the three-valve assembly and the differential pressure transmitter are connected together first, and then this combined unit is installed at the end of the pressure sensing tubes. When in use, the three valves of the three-valve assembly are used together. During testing, to prevent a sudden increase in pressure at the sensors on both sides as the medium enters the pressure sampling tubes, thereby increasing the pressure difference, it is necessary to first open the balance valve located in the middle of the three-valve assembly and close the pressure sampling valves on both sides. Once the pipeline is filled with the medium and the pressures on both sides stabilize, the pressure sampling valves on both sides can be slowly opened to allow the pressures to change at a constant rate. Finally, the balance valve is closed, and the flow meter begins to function properly. The three-valve assembly is used in conjunction with differential pressure flowmeters during zero adjustment; the balance valve must be opened while the pressure-taking valves on both sides are closed in order to carry out the zero-point adjustment.