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# Precautions for installation of orifice flowmeter

by：Sure     2021-08-03
1. Pipeline conditions: (1) The straight pipe sections before and after the throttle must be straight, and there must be no visible bends. (2) The straight pipe section used to install the throttle should be smooth. If not, the flow coefficient should be multiplied by the roughness to correct the sparseness. (3) In order to ensure that the flow of fluid forms a fully developed turbulent velocity distribution 1D before the throttle, and make this distribution into a uniform axis 1. Pipeline conditions: (1) The straight pipe sections before and after the throttle must be Straight, there must be no visible curvature. (2) The straight pipe section used to install the throttle should be smooth. If it is not smooth, the flow coefficient should be multiplied by the roughness to correct the sparseness. (3) In order to ensure that the flow of fluid forms a fully developed turbulent velocity distribution 1D in front of the throttling piece, and to make this distribution a uniform axisymmetric shape, 1) the straight pipe section must be round, and the throttling The roundness of the 2D range in front of the piece is very strict, and there is a certain roundness index. Specific measurement method: (A) On the 4 vertical pipe sections OD, D/2, D, 2D before the throttle, measure the inner diameter of at least 4 pipes with the same angular distance, and take the average value D. The difference between any single measured value of inner diameter and the average value shall not exceed ±0. 3% (B) After the throttle, 8 single measured values u200bu200bof inner diameter are measured by the above method at OD and 2D positions, and any single measured value is compared with D , The maximum deviation shall not exceed ±2% 2) A sufficiently long straight pipe section is required before and after the throttling piece. This section of straight pipe section is required to be related to the form of the local resistance piece in front of the throttling piece and the diameter ratio β, see Table 1 (Βu003dd/D, d is the hole diameter of the orifice, and D is the inner diameter of the pipe). (4) The length of the straight pipe section between the first resistance element and the second resistance element on the upstream side of the throttling element can be in the form of the second resistance element and βu003d0. 7 (regardless of the actual β value) as listed in Table 1. 1/2 of the value (5) when the upstream side of the throttling piece is an open space or a large vessel with a diameter ≥ 2D, the open space or the straight pipe length between the large vessel and the throttling piece shall not be less than 30D (15D) if the throttling piece When there are other local resistance parts between the open space or the large container, in addition to the minimum straight pipe length 1 specified in Table 1 between the throttling part and the local resistance part, from the open space to the throttling The total length of the straight pipe section between the pieces shall not be less than 30D (15D). The minimum straight pipe length on the upstream and downstream sides of the throttling element is shown in Table 1. The form of the local female component on the upstream side of the throttling element and the minimum straight pipe length L Note: 1. The above table is only for standard throttling devices, but for special throttling devices. For reference 2. The number of columns is a multiple of the inner diameter D of the pipe. 3. The numbers outside the parentheses in the above table are the values u200bu200bof 'additional relative limit error is zeroThat is, when there is a value in parentheses in the length of the straight pipe section, the limit relative error τQ/Q of the flow measurement. Add 0.5% arithmetic again, that is (τQ/Q+0.5)%4. If the actual straight pipe length is greater than the value in the brackets but less than the value outside the brackets, it needs to be treated as 'additional limit relative error 0.5%'. (1) The front end face of the DC component installed in the pipeline must be perpendicular to the axis of the pipeline, and the maximum allowable non-perpendicularity shall not exceed ±1°. (2) After the throttle is installed in the pipeline, its opening must be concentric with the pipeline, and the maximum allowable misalignment ε shall not exceed the calculation result of the following formula: ε≤0.015D (1/β-1). (3) All gaskets should not be made of too thick material, preferably no more than 0.5mm. The gasket should not protrude into the pipe wall, otherwise it may cause a large measurement error. (4) All valves used to adjust the flow rate should be installed beyond the minimum length of the pipe section after the throttle. (5) The installation of the throttling device on the process pipeline must be carried out after the pipeline is cleaned and purged. (6) The pressure taking method of the throttling device installed in the horizontal or inclined pipeline. 1) When the measured fluid is a liquid, in order to prevent bubbles from entering the process pipeline and reaching the jaws, the pressure buckle should be at a position where the center line of the process pipeline is offset ≤45°, and the positive or negative value is αα　α1
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