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Why cannot the flow orifice plate be installed in reverse? This is because: when the orifice plate is installed correctly, its throat faces in the direction of fluid flow. The fluid contracts locally at the orifice center, which increases the flow velocity and reduces the static pressure; as a result, a static pressure difference is created before and after the orifice, and this pressure difference has a certain functional relationship with the flow rate. When the orifice plate is installed in reverse, its inlet face assumes a conical shape. As a result, the degree of contraction of the fluid as it passes through the orifice plate is less compared to when it is installed correctly; moreover, the location where the flow stream narrows is farther away from the orifice plate than in the correct installation. The velocity of the fluid as it passes through the rear face of the orifice plate is also lower than in the correct installation, which leads to a higher pressure behind the orifice plate. This in turn reduces the static pressure difference before and after the orifice plate, causing the measured flow rate to decrease and affecting the accuracy of flow measurement. Therefore, if the positive and negative directions of the orifice plate flow meter are reversed, it will lead to measurement errors, either no measurement results being obtained or the flow rate value being negative. Hence, it is essential to pay attention to the positive and negative directions when installing an orifice plate flow meter. The orifice plate flow meter is one type of differential pressure flow meter; therefore, it calculates flow rates based on the principle of differential pressure. As a result, if the positive and negative directions are reversed, a pressure reduction effect cannot be achieved, which in turn leads to a smaller pressure difference across the orifice plate. Working principle of the orifice flow meter: When a fluid fills a pipe and flows through a throttling element within it, the flow stream contracts locally, which increases the flow velocity and reduces the static pressure. As a result, a pressure drop, or differential pressure, is generated before and after the throttling element. The greater the flow rate of the fluid, the larger the pressure difference created before and after the throttling element; therefore, the orifice flow meter can measure the flow rate of the fluid by detecting this pressure difference. This measurement method is based on the law of conservation of energy and the law of continuity of flow. Working characteristics: ① The throttle device has a simple and robust structure, stable and reliable performance, a long service life, and is inexpensive ； ②It has a wide range of applications; it can measure all types of single-phase flows, and can also be used for some mixed-phase flows ； ③The standard throttle device can be put into use without the need for actual flow calibration ； ④The integrated orifice plate is easier to install; it requires no pressure lead pipes, and can be connected directly to differential pressure transmitters and pressure transmitters.