What are the requirements for selecting and installing an average velocity tube flow meter?

Flow rate range, temperature, pressure, density, etc. The installation is determined by the flow meter based on the selected principle. Basically, it consists of straight sections at the front and back, which are concentric and coaxial, avoiding components such as pumps.

At the installation location on the pipe, insert the sensor into the pipe and secure it in place. It is important to pay attention to the direction of fluid flow; the arrow indicated on the velocity tube should be aligned with the direction of the fluid flow. Additionally, the total pressure sensing hole on the sensor (the side with more openings on the sensor rod) must be facing directly at the fluid.

The straight pipe section meets the requirements; the flow direction is correct and perpendicular to the centerline of the pipe. When measuring gases, the pressure tap should face upward, while when measuring liquids, it should face downward. The installation of the pressure guiding tubes follows the same requirements as those for orifice plate flow meters. Refer to SH/T 3551-2013 \"Code for Acceptance of Construction Quality of Petrochemical Instrumentation Projects\"

1. Provide correct flow and pipeline data. The mechanical dimensions of the differential pressure averaging tube flow meter are customized according to the size of the pipeline in which it is to be installed, while its measurement range is calculated and calibrated based on the flow data provided by the process. When selecting, it is essential to provide the manufacturer with the correct flow rate data and pipe dimensions, which include the outer diameter and wall thickness. 2. Choose the testing rod correctly. The main component of a differential pressure type average velocity tube flow meter is an inserted sensing rod, which comes in various forms with different cross-sectional shapes, such as circular tubes, diamond-shaped tubes, and Delta-shaped tubes. Since different shapes of sensing rods correspond to various fluid dynamics theories, it is necessary to use a high-precision differential pressure transmitter. The differential pressure type venturi flow meter calculates flow rate by measuring the total static pressure; it is commonly used for measuring gas flow rates in large-diameter pipes. The differential pressure generated by this type of meter is usually quite low, with a minimum of only 20–30 pascals. It is advisable to avoid using pressure tapping tubes and instead opt for high-precision differential pressure transmitters such as the 3051 model (my previous company used venturi meters combined with 3051 transmitters for measuring steam flow). The best approach is to use an integrated system that combines a venturi meter, a three-valve assembly, and a differential pressure transmitter in one unit. This not only reduces leaks caused by the use of pressure tapping tubes but also helps to compensate for distortions in the differential pressure signal resulting from changes in temperature and pressure. 4. Ensure a certain length of straight pipe section. In a differential pressure type venturi flow meter, the pipe section ahead of it must have a straight section whose length is 7 to 9 times the diameter of the pipe; various sources provide different values for this ratio, ranging from 3 to 30 times. Only by ensuring such a length can the gas flow velocity within the large pipe be as evenly distributed as possible along the axis. Only in this way can the flow rate through the entire cross-section be determined by measuring the velocity at just a few points. Otherwise, the flow velocity distribution within the large pipe becomes very complex, resulting in large fluctuations in the flow coefficient K, which undermines the accuracy of the measurements. 5. Repeatability and accuracy. In some factories, the venturi flow meter serves merely as a sensing element that provides information at a certain process point; it outputs data reflecting the gas flow rate. It is not necessary for this value to be exact, but rather it is important that it accurately reflects any changes in the flow rate. This requires the venturi to function reliably, with its output maintaining a consistent functional relationship with the flow rate, thus ensuring good repeatability. If the straight pipe section does not meet the requirements, the repeatability can reach 0.5%, while the error may exceed 6%. In automated systems for regulation and monitoring, differential pressure average velocity tube flowmeters with a simple structure offer advantages. 6. Install necessary dust filtration devices. If the processing process is particularly complex, such as when there is a high level of dust, it is recommended to install necessary auxiliary equipment, such as dust filtration systems, to prevent the uniform velocity tube from getting clogged and thus ensure the proper functioning of the instruments.

It is mainly a cleaning medium; the pressure difference measured is too small, resulting in average accuracy