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Industry Information
Precautions for daily maintenance and installation of orifice flowmeters
2012-3-7 9:24:35


的日常维护包括: Orifice plate flowmeter routine maintenance includes:

1: Manual zero adjustment method: refers to the manual zero adjustment of the differential pressure transmitter using a multimeter. This method can be used when the zero point of the differential pressure transmitter drifts slightly. The method is as follows: And negative two signal lines, remove one of them, adjust the multimeter to the 4-20mA DC position, string the multimeter in, and the differential pressure transmitter has a zero adjustment screw (the zero mark on the top is the zero adjustment button). Debugging with the hour hand will increase the current and decrease it counterclockwise. When the multimeter displays 4mA, the zero point will be adjusted at this time.

2: Valve opening and closing sequence during condensation (mainly for steam): during normal operation, the middle valve of the three-valve group is closed, and the two sides of the valve are open. If sewage or re-condensation is required, first close the two sides of the valve, and then open the middle valve. Finally, open the root drain valve to drain. If the condensation is complete, you want to close the middle valve, and then open the two valves slowly, the system is in normal operation.
3: When the measurement medium is steam, online zero adjustment should be performed, because the condensation plate may have a slight height difference during installation, and when the flow velocity of the measurement fluid is small, its height difference has a greater impact on the flow rate at this time. (1 cm water column is 100Pa)

安装注意事项: Note for orifice plate flow meter installation:
1. Pipeline conditions:
(1) The straight pipe section before and after the throttle must be straight, and there must be no visible bend.
(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 to correct the sparseness.
(3) In order to ensure that the movement of the fluid 1D in front of the throttle constitutes a sufficient spread of the turbulent velocity, and to make this dispersion into an average axisymmetric shape, the straight pipe section must be round, and the front of the throttle must be round. The 2D range requires its roundness to be severe and has a certain roundness target. Detailed weighing method:
(A) On the four vertical pipe sections of OD, D / 2, D, and 2D in front of the throttle, discriminate and measure up to 4 single diameters of the inner diameter of the pipe at most equal angular intervals, and take the uniform value D. The difference between the single inner diameter measurement value and the uniform value must not exceed ± 0.3%
(B) After the throttling part, 8 single-diameter single-measurement values were measured at the OD and 2D positions using the above method. The intentional single-measurement value is comparable to D, and its maximum deviation must not exceed ± 2%.
2) A long straight pipe section is required before and after the throttle. This long straight pipe section is related to the part of the resistance member in front of the throttle and the diameter ratio β, as shown in Table 1 (β = d / D, d is Orifice plate opening diameter, D is the inner diameter of the pipe).
(4) The length of the straight pipe section between the first resistance member and the second resistance member on the downstream side of the throttling member can be listed in Table 1 according to the manner of the second resistance member and β = 0. 7 (regardless of the practice β value). 1/2 of the value
(5) When the downstream side of the throttle is a closed space or a large container with a diameter ≥ 2D, the length of the straight pipe between the closed space or the large container and the throttle shall not be less than 30D (15D). When there are other partial resistance members between the containers, in addition to the minimum straight pipe length 1 attached to the table in Table 1 between the throttle and some resistance members, the straight from the closed space to the throttle The total length of the pipe section must not be less than 30D (15D).
Minimum straight pipe length on the upstream and downstream sides of the throttle table 1
Method of female force part and minimum straight pipe length L on the downstream side of the throttle


备注:1、上表只对规范节流安装而言,对特殊节流安装可供参考 Remarks for orifice flowmeter : 1. The above table is only for the specification of throttling installation, and for special throttling installation for reference
2. The number of columns is a multiple of the inner diameter D of the tube.
3. The numbers outside the parentheses in the table above are the values of "additional absolute limit error is zero", and the numbers in parentheses are the values of "additional absolute limit error is ± 0.5%". That is, when one of the straight pipe lengths uses the value in parentheses, the limit absolute error τQ / Q of flow measurement. Should be arithmetically added by 0.5%, which is (τQ / Q + 0.5)%
4. If the length of the straight pipe segment in practice is greater than the value in the brackets and smaller than the value outside the brackets, it shall be handled according to the "additional limit absolute error is 0.5%".
(1) When the DC component is installed in the pipeline, its front end surface must be perpendicular to the pipeline axis, and the maximum non-verticality allowed must not exceed ± 1 °.
(2) After the throttling device is installed in the pipeline, its opening must be concentric with the pipeline, and its maximum allowed misalignment ε must not exceed the following formula to calculate the consequences: ε ≤ 0.015D (1 / β-1).
(3) All gaskets should not use too thick materials, it is better not to exceed 0.5mm. The gaskets cannot protrude inside the pipe wall, otherwise it can cause a large measurement error.
(4) Any valve for regulating flow should be installed beyond the minimum pipe length after the throttle
(5) The device for throttling the installation on the process pipeline must be stopped after the pipeline is cleaned and purged.
(6) The pressure-receiving method of throttling installation in the degree or inclined pipe device.
1) When the fluid to be measured is liquid, in order to avoid air bubbles from entering the process pipeline to the teeth, the pressure buckle should be taken at a position ≤45 ° below the centerline of the process pipeline.