1. Pipeline conditions:
(1) The straight pipe sections before and after the throttle piece must be straight and must not be visible to the naked eye.
(2) The straight pipe section used for installing the throttle piece should be smooth. If it is not smooth, the flow coefficient should be multiplied by the roughness correction sparse.
(3) In order to ensure the flow of fluid in the 1D before the throttle to form a fully developed turbulent velocity distribution, and to make this distribution a uniform axisymmetric shape, 1) the straight pipe section must be round and throttled The range of the front 2D, its roundness requires very strict, and has a certain roundness index. Specific measurement method:
(A) On the OD, D/2, D, and 2D vertical tube sections of the throttle, the measured values ​​of the inner diameters of the four pipes are measured at least equal angular distances, and the average value D is taken. The difference between the measured value of any internal diameter and the average value shall not exceed ±0.3%.
(B) After the throttle, 8 internal diameter single measurements are measured by the above method at the OD and 2D positions. The maximum single deviation is not more than ±2% compared with D. 2) A section is required before and after the throttle A straight pipe section of sufficient length, the length of the straight pipe section long enough and the form of the local resistance part before the throttle element are related to the diameter ratio β, see Table 1 (β=d/D, d is the orifice diameter of the orifice, D is Pipe inner diameter).
(4) The length of the straight pipe section between the first resistance member and the second resistance member on the upstream side of the throttle member may be in the form of the second resistance member and β = 0.7 (regardless of the actual β value), which is listed in Table 1. 1/2 of the value
(5) When the upstream side of the throttle member is an open space or a large container with a diameter ≥ 2D, the open space or the straight pipe length between the large container and the throttle member shall not be less than 30D (15D) if the throttle member and the open space or large When there are other local resistance members between the containers, the straight line between the open space and the throttle member is provided, except that the minimum straight pipe length specified in Table 1 is attached between the throttle member and the local resistance member. The total length of the pipe section must not be less than 30D (15D).
The length of the smallest straight pipe section on the upstream and downstream side of the throttle piece Table 1 The form of the local negative force part on the upstream side of the throttle piece and the minimum straight pipe length L Note:
1. The above table is only for standard throttling devices. For special throttling devices, reference is available.
2. The number of columns is a multiple of the inner diameter D of the tube.
3. The number outside the parentheses in the above table is the value of “additional relative limit error is zeroâ€, and the number in parentheses is the value of “additional relative limit error is ±0.5%â€. That is, when there is a value in the brackets in the length of the straight pipe, the limit relative error Ï„Q/Q of the flow measurement. The arithmetic should be added by 0.5%, which is (Ï„Q/Q+0.5)%.
4. If the length of the actual straight pipe section is larger than the value in parentheses and less than the value outside the brackets, it shall be treated according to the “additional limit relative error of 0.5%â€.
(1) The DC component is installed in the pipeline, and its front end surface must be perpendicular to the pipe axis, and the maximum allowable non-perpendicularity shall not exceed ±1°.
(2) After the throttle is installed in the pipeline, the opening must be concentric with the pipeline, and the maximum allowable degree of ε allowed by the throttle shall not exceed the calculation result of the following formula: ε ≤ 0.015D (1/β-1).
(3) All gaskets should not be used with too thick materials, not exceeding 0.5mm. The gaskets cannot protrude inside the pipe wall or it may cause a large measurement error.
(4) All valves used to adjust the flow rate shall be installed outside the minimum length of the pipe section after the throttle (5) The installation of the throttling device on the process pipe shall be carried out after the pipe cleaning and purging.
(6) The pressure-receiving method of the throttling device installed in the horizontal or inclined pipe.
1) When the fluid to be tested is a liquid, in order to prevent air bubbles from entering the process pipe into the teeth, the pressure button should be at the position where the center line of the process pipe is ≤45°, and the αα α1 is taken.
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