Seven key points for measuring liquids and gases using metal tube float flow meters
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Metal tube float flowmeter, also known as metal rotor flowmeter, is widely used for measuring medium, small and micro flow rates. The measuring medium is generally clean, not easy to crystallize and solidify, low viscosity liquids, gases, and vapors, requiring slow changes in medium flow rate. The correct installation of instruments is fundamental to ensuring their stable operation in the future. Whether the instruments can be installed correctly is an important indicator that tests the technical personnel of instrument installation. In response to various influencing factors encountered during installation, this article introduces the following factors that should be paid attention to when installing metal tube float flow meters to friends The installation direction of most float flow meters must be installed vertically on vibration free pipelines, without obvious tilting, and the fluid should flow through the instrument from bottom to top. It is said to be an example of pipeline connection, equipped with a bypass pipe system for maintenance without interruption of flow. The angle between the centerline of the float flowmeter and the plumb line generally does not exceed 5 degrees, and it is a high-precision (1.5 or above) instrument θ≤ 20 °. If θ= 12 ° will result in an additional error of 1%. There is no strict upstream straight pipe length requirement for instruments, but there are also manufacturers who require a (2-5) D length, which is actually not necessary. 2, Filters should be installed upstream of the instrument for the installation of dirty fluids. When a metal tube float flowmeter with magnetic coupling is used for fluids that may contain ferromagnetic impurities, a magnetic filter should be installed in front of the instrument. To maintain the cleanliness of the float and cone, especially for small caliber instruments, the cleanliness of the float significantly affects the measurement value. For example, a 6mm diameter glass float flowmeter measures seemingly clean water in the laboratory, with a flow rate of 2.5L/h. After 24 hours of operation, the flow rate reading increases by a few percent. There are foreign objects on the surface of the float that cannot be observed by the naked eye. The float is removed and wiped with gauze to restore the original flow rate reading.
3, The installation of pulsating flow involves the pulsation of the flow itself. If there is a reciprocating pump or regulating valve upstream of the intended instrument installation position, or there is a significant load change downstream, the measurement position should be changed or remedial improvements should be made in the pipeline system, such as adding a buffer tank; If there is oscillation in the instrument itself, such as low gas pressure during measurement, incomplete opening of upstream valves, and failure to install regulating valves downstream of the instrument, targeted improvements should be made to overcome it, or instruments with damping devices should be selected instead. 4, Expansion of Range Installation: If the required flow range for measurement is wide, and the range exceeds 10, two or more glass tube float flow meters with different flow ranges are often used in parallel. According to the measurement, one or more instruments are selected to be connected in series. When the flow rate is low, the indicated value of the flow range meter is read, and when the flow rate is high, the indicated value of the flow rate meter is read. The series connection method is easier to operate than the parallel connection method, and there is no need to frequently open and close valves, but the pressure loss is large. You can also place two floats of different shapes and weights inside the instrument panel. When the flow rate is low, take a light float reading, and when the float reaches the top, take a heavy float reading. The range can be expanded to 50-100. 5, To drain the liquid, use an angle metal float flowmeter with gas inlet and outlet not in a straight line in the instrument. When using it for liquid, pay attention to whether there is residual air in the extended sleeve of the external float displacement, and it must be drained; If the liquid contains small bubbles that are prone to accumulate inside the casing during flow, it is even more important to exhaust at regular intervals. This is more important for small caliber instruments, otherwise it will significantly affect the flow indication. 6, If necessary conversion is not made based on the parameters of the medium such as density and viscosity, instruments specially customized for the manufacturing plant, liquid instruments are usually calibrated for flow rate with water, gas instruments are calibrated with air, and the fixed value is in the engineering standard state. When the fluid density, gas pressure and temperature under different usage conditions are not consistent with calibration, necessary conversions should be made. The conversion formulas and methods are detailed in the user manuals of each manufacturing plant. 7, Verification and calibration of float flow meters commonly used liquid standard meter method, volumetric method, and weighing method; The commonly used gas method is the bell jar method, while the soap film method is used for small flow rates. Some bulk products from external manufacturing plants have achieved dry calibration, which involves controlling the size of the conical tube and the weight size of the float, indirectly determining the flow value, in order to reduce costs, and only high-precision instruments are calibrated in real flow. Some manufacturers also strictly control the inner diameter and taper of the starting point of the conical tube, as well as the size of the float. Real flow verification only serves to check the quality of the inner surface of the conical tube. The instruments, conical tubes, and floats produced by such manufacturers have been interchangeable and do not require complete replacement. The use of standard meter calibration for float flow meters is an efficient method that has been applied in various manufacturing plants. Some manufacturers produce glass tube float flowmeters with several sections of smaller taper using standard meters within a certain flow range. By extending the length of the standard meter scale and improving the accuracy of the standard meter, the calibration work can achieve high precision and efficiency.
