Precautions for installation of orifice flowmeter:
1. Pipeline conditions:
(1) The straight pipe section before and after the throttling element must be straight and there must be no visible bending.
(2) The straight pipe section used for throttling devices should be lubricated. If not lubricated, the flow coefficient should be multiplied by the roughness to correct for sparsity.
(3) In order to ensure that the fluid's activity forms a sufficient turbulent velocity dispersion in front of the throttling element 1D, and to make this dispersion an average axisymmetric shape
1) The straight pipe section must be circular, and the roundness requirements for the 2D range of the throttling element are very strict, with a certain roundness target. Detailed weighing method:
(A) On the four vertical pipe sections OD, D/2, D, and 2D in front of the throttling element, at most four single inner diameter measurements of the pipes should be distinguished and measured at equal angular intervals, and the uniform value D should be taken. The difference between any single inner diameter measurement value and the uniform value should not exceed ± 0. 3%
(B) After the throttling element, 8 single inner diameter measurements were obtained using the above method at the OD and 2D positions. Any single measurement can be compared with D, and its deviation should not exceed ± 2%
2) A sufficiently long straight pipe section is required before and after the throttling element, which is related to the resistance element in front of the throttling element and the diameter ratio β, as shown in Table 1 (β=d/D, where d is the diameter of the orifice plate opening and D is the inner diameter of the pipeline).
(4) The length of the straight pipe section between the downstream resistance element of the throttling element and the second resistance element can be adjusted in the same way as the second resistance element and β=0. 7 (regardless of the actual beta value) take half of the values listed in Table 1
(5) When the downstream side of the throttling element is a closed space or a large container with a diameter ≥ 2D, the length of the straight pipe between the closed space or large container and the throttling element shall not be less than 30D (15D). If there are other resistance elements between the throttling element and the closed space or large container, in addition to the small straight pipe section length 1 that conforms to the rules in Table 1, the total length of the straight pipe section from the closed space to the throttling element shall not be less than 30D (15D).
Table 1 Length of small straight pipe sections on the upstream and downstream sides of the throttling element
The downstream part of the throttling element adopts the negative force element method and the length of the small straight pipe section L
Note: 1. The above table is only for standardized throttling installation and can be used as a reference for throttling installation
2. The column number system is a multiple of the inner diameter D of the tube.
3. The number outside the parentheses in the table represents the value of "zero additional limit error", and the number inside the parentheses represents the value of "± 0.5% additional limit error". When there is a value in parentheses in the length of the straight pipe section, the limit error of flow measurement is τ Q/Q. The arithmetic addition should be 0.5%, which is (τ Q/Q+0.5)%
4. If the length of the straight pipe section in practice is greater than the value in parentheses but less than the value outside parentheses, it should be treated as "additional limit error of 0.5%".
(1) The DC component device must be installed in the pipeline, and its front end face must be perpendicular to the pipeline axis. The allowable deviation from perpendicularity must not exceed ± 1 °.
(2) After the throttle device is installed in the pipeline, its opening must be concentric with the pipeline, and the allowable large eccentricity ε must not exceed the following formula to calculate the consequences: ε ≤ 0.015D (1/β -1).
(3) All gaskets should not use materials that are too thick, not exceeding 0.5mm. The gasket should not protrude from the pipe wall, otherwise it can cause significant measurement errors.
(4) Any valve used for regulating flow should be installed beyond the length of the small value pipe section behind the throttling element
(5) The device installed on the process pipeline for throttling must be stopped after pipeline cleaning and blowing.
(6) The pressure tapping method for throttling installation of pipeline devices with degree or inclination.