Orifice flowmeter installation precautions:
1. Orifice flowmeter pipeline conditions:
(1) Straight pipe sections before and after the throttle element must be straight and must not be visible to the naked eye.
(2) The straight pipe section of the device throttle should be lubricated. If it is not lubricated, the flow coefficient should be multiplied by the roughness correction sparse.
(3) In order to ensure that the fluid activity is spread in the 1D front of the throttle to form a sufficient turbulent velocity, and this is spread into an average axisymmetric shape,
1) The straight pipe section must be round, and for the front 2D range of the throttle, its roundness is required to be severe and has a certain roundness goal. Detailed trade-offs:
(A) On the OD, D/2, D, 2D 4 vertical pipe sections of the throttle, measure the inner diameter of the four pipes at most equal to each other at an equal angular interval, and take a uniform value D. The difference between the measured value and the uniform value of the free inner diameter shall not exceed ±0.3%.
(B) After the throttle, in the OD and 2D position, 8 internal diameter single measurements are measured by the above method, and the single measured value is compared with D, and the maximum deviation must not exceed ±2%.
2) Before and after the throttle, a straight pipe section of sufficient length is required. The length of the straight pipe section and the part of the resistance part before the throttle are related to the diameter ratio β, see Table 1 (β=d/D, d is Orifice opening diameter, D is the inner diameter of the pipe).
(4) The length of the straight pipe between the first resistance member and the second resistance member on the downstream side of the throttle member can be taken as the second resistance member and β = 0.7 (regardless of the practice β value), the values ​​listed in Table 1 are taken. 1/2
(5) When the downstream side of the throttle piece is a closed space or a large container with a diameter ≥ 2D, the closed pipe length between the closed space or the large container and the throttle piece shall not be less than 30D (15D) if the throttle piece and the closed space or large When there are other partial resistance members between the containers, the straight line between the closing space and the throttle member is provided, except that the minimum straight pipe length 1 attached to the rule on Table 1 is provided between the throttle member and the partial 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 negative force part of the downstream part of the throttle piece and the minimum straight pipe length L Note: The orifice flowmeter is also widely used in the compression hole flow measurement, so the compressed air is measured. Users of the flow should pay special attention to the installation method of the orifice flowmeter.
1, the above table is only for the standard throttling installation, for special throttling installation for reference
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 absolute limit error is zeroâ€, and the number in parentheses is the value of “additional absolute 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 absolute 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 straight pipe is more than the value in parentheses and less than the value outside the brackets, it should be disposed according to the “additional limit absolute error of 0.5%â€.
(1) The DC component device shall have a front end face perpendicular to the pipe axis in the pipe, and the maximum allowable non-perpendicularity shall not exceed ±1°.
(2) After the throttle device is installed in the pipeline, its opening must be concentric with the pipeline, and the maximum divergence ε allowed may not exceed the following formula: ε ≤ 0.015D (1/β-1).
(3) All gaskets can not use too thick data, it is best not to exceed 0.5mm, the gasket can not protrude inside the pipe wall or it can cause a large measurement error.
(4) Where the valve for regulating flow rate is to be installed outside the length of the minimum pipe section after the throttle
(5) Throttling devices installed on the process piping must be stopped after the pipe cleaning purge.
(6) The pressure-receiving method of the intelligent flowmeter in the throttling installation of the degree or inclined pipeline device. 1) When the fluid to be tested is liquid, in order to prevent air bubbles from entering the process pipeline, the pressure button should be in the position of ≤45° under the center line of the process pipe.
1. Orifice flowmeter pipeline conditions:
(1) Straight pipe sections before and after the throttle element must be straight and must not be visible to the naked eye.
(2) The straight pipe section of the device throttle should be lubricated. If it is not lubricated, the flow coefficient should be multiplied by the roughness correction sparse.
(3) In order to ensure that the fluid activity is spread in the 1D front of the throttle to form a sufficient turbulent velocity, and this is spread into an average axisymmetric shape,
1) The straight pipe section must be round, and for the front 2D range of the throttle, its roundness is required to be severe and has a certain roundness goal. Detailed trade-offs:
(A) On the OD, D/2, D, 2D 4 vertical pipe sections of the throttle, measure the inner diameter of the four pipes at most equal to each other at an equal angular interval, and take a uniform value D. The difference between the measured value and the uniform value of the free inner diameter shall not exceed ±0.3%.
(B) After the throttle, in the OD and 2D position, 8 internal diameter single measurements are measured by the above method, and the single measured value is compared with D, and the maximum deviation must not exceed ±2%.
2) Before and after the throttle, a straight pipe section of sufficient length is required. The length of the straight pipe section and the part of the resistance part before the throttle are related to the diameter ratio β, see Table 1 (β=d/D, d is Orifice opening diameter, D is the inner diameter of the pipe).
(4) The length of the straight pipe between the first resistance member and the second resistance member on the downstream side of the throttle member can be taken as the second resistance member and β = 0.7 (regardless of the practice β value), the values ​​listed in Table 1 are taken. 1/2
(5) When the downstream side of the throttle piece is a closed space or a large container with a diameter ≥ 2D, the closed pipe length between the closed space or the large container and the throttle piece shall not be less than 30D (15D) if the throttle piece and the closed space or large When there are other partial resistance members between the containers, the straight line between the closing space and the throttle member is provided, except that the minimum straight pipe length 1 attached to the rule on Table 1 is provided between the throttle member and the partial 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 negative force part of the downstream part of the throttle piece and the minimum straight pipe length L Note: The orifice flowmeter is also widely used in the compression hole flow measurement, so the compressed air is measured. Users of the flow should pay special attention to the installation method of the orifice flowmeter.
1, the above table is only for the standard throttling installation, for special throttling installation for reference
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 absolute limit error is zeroâ€, and the number in parentheses is the value of “additional absolute 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 absolute 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 straight pipe is more than the value in parentheses and less than the value outside the brackets, it should be disposed according to the “additional limit absolute error of 0.5%â€.
(1) The DC component device shall have a front end face perpendicular to the pipe axis in the pipe, and the maximum allowable non-perpendicularity shall not exceed ±1°.
(2) After the throttle device is installed in the pipeline, its opening must be concentric with the pipeline, and the maximum divergence ε allowed may not exceed the following formula: ε ≤ 0.015D (1/β-1).
(3) All gaskets can not use too thick data, it is best not to exceed 0.5mm, the gasket can not protrude inside the pipe wall or it can cause a large measurement error.
(4) Where the valve for regulating flow rate is to be installed outside the length of the minimum pipe section after the throttle
(5) Throttling devices installed on the process piping must be stopped after the pipe cleaning purge.
(6) The pressure-receiving method of the intelligent flowmeter in the throttling installation of the degree or inclined pipeline device. 1) When the fluid to be tested is liquid, in order to prevent air bubbles from entering the process pipeline, the pressure button should be in the position of ≤45° under the center line of the process pipe.
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