3.4　Flow

3.4.1　The installation of flow measuring throttled device shall meet those specified in"Measurement of Fluid Flow by Means of Pressure Differential Devices Inserted in Circular Cross-section Conduits Running Full-Part 1～Part 4"（GB/T 2624.1～4）.

3.4.2　Before installation，the appearance of throttled device and the diameter of throttling orifice shall be inspected and measured，and the relevant records shall be made.The appearance，material and dimension of throttled device shall meet those specified in the"Measurement of Fluid Flow by Means of Pressure Differential Devices Inserted in Circular Cross-section Conduits Running Full-Part 1～Part 4"（GB/T 2624.1～4）.

3.4.3　The minimum length of the straight pipe sections at upstream and downstream of the throttled device shall meet those specified in Appendix B.

3.4.4　The throttled device shall be installed at the upstream of the adjacent throttled device and within the length range of at least 2 times of the pipeline inside diameter，its average deviation value of any cross section within the inside diameter of pipeline shall be±0.3%.

3.4.5　Within the length range of at least 10 times of pipeline inside diameter at upstream and at least 4 times of pipeline inside diameter at downstream of throttled device，the internal surface of pipe shall be clean and shall meet the requirements of roughness parameter.

3.4.6　Every pressure measuring device of the throttled device shall have at least one upstream pressure tapping and one downstream pressure tapping that have the same diameter.For different pressure measuring modes，the position and diameter of the upstream and downstream pressure tapping shall meet those specified in the"Measurement of Fluid Flow by Means of Pressure Differential Devices Inserted in Circular Cross-section Conduits Running Full-Part 1～Part 4"（GB/T 2624.1～4）.

3.4.7　The axis of the pressure tapping of throttled device shall be intersected with and be perpendicular to the axis of pipeline.The inner edge of pressure tapping shall be parallel with the inner wall of pipeline.

3.4.8　When measuring the differential pressure of throttled device by using equalizing ring，the quantity of the pressure holes at the upstream and downstream sides shall be equal，the pressure holes at the same side shall be set uniformly on one cross section.

3.4.9　Throttled device installed in the pipeline shall be perpendicular to the axis of pipeline.

3.4.10　Where the retainer ring is adopted，any part of the retainer ring shall not be intruded into the pipeline；if the washer is used between the throttled device and the retainer ring，the washer shall not be intruded into the retainer ring.

3.4.11　When the throttled device is adopted with angle joint pressure measuring device，the washer shall not block the pressure tapping or trough.

3.4.12　When the throttled device is installed on horizontal or inclined pipeline and the flow medium is gas or liquid，then the orientation of pressure tapping shall meet those specified in Item 1 and Item 2 of 3.3.2 of this Part.

3.4.13　The condensers installed at the upstream and downstream pressure tapping of throttled device for measuring steam flow shall meet the design requirements.When installing，the liquid level of two condensers shall be at the same height and shall not be lower than the pressure tapping.Where the differential pressure instrument is higher than the throttled device，the condenser shall be higher than the differential pressure instrument，and the pipe from the condenser to throttled device shall be insulated.

3.4.14　As for the throttled device installed on horizontal or inclined steam pipeline，the orientation of its pressure tapping shall be within the scope of 45° included angle upward from the horizontal center line of pipeline.

3.4.15　As for the newly installed pipeline system，the installation of throttled device shall be carried out after the pipeline is washed until being qualified.

3.4.16　As for the annubar flowmeter，its axis shall be intersected with the pipeline axis at right angle.When inserting the uniform velocity pipe into the pipeline，the dynamic pressure hole shall face to the flow direction of the medium，the center line of static hole shall be superposed with the central axis of pipeline，and the length of the straight pipe sections before and after the uniform velocity pipe shall meet the requirements of the manufacturer's technical document.

3.4.17　The length of the straight pipe sections before and after the compound venturi air volume measuring device shall meet the requirements of the manufacturer's technical document.

3.4.18　The length of straight pipe section before the wing-type air volume measuring device shall not be less than 0.6 times of its equivalent diameter，and the length of its subsequent straight pipe section shall be 0.2 times of its equivalent diameter.The center line of measuring device shall be superposed with the center line of air duct，two or more wing-type pilot pipes shall be installed at the same measuring point on the air duct，and the static holes shall be on the same cross section.

3.4.19　The target type flowmeter should be installed on horizontal pipeline.Where it must be installed on vertical pipeline，the flow medium direction shall be upward.The center of target shall be on the axis of process pipe section.

3.4.20　The rotameter shall be vertically installed，its inclination shall not exceed 2° for Class 1.0 and Class 1.5 flowmeters and shall not exceed 5° for flowmeters below Class 1.5，the flow medium shall pass through the flowmeter from bottom to top.The length of upstream straight pipe section should not be less than 5 times of the inside diameter of process pipeline.

3.4.21　The installation of velocity flow meters，namely the sensors like turbine flowmeter，vortex shedding flow meter，vortex flowmeter，electromagnetic flowmeter and ultrasonic flowmeter，shall meet the following requirements：

1　As for the upstream and downstream straight pipe sections of flowmeter，their lengths shall meet the provisions of manufacturer，and the difference between their inside diameter and the nominal diameter of flowmeter shall neither exceed±3% of the nominal diameter nor exceed±5mm；as for the flowmeters with accuracy below Class 0.5，the inner wall of straight pipe section within length scope of 10 times of nominal diameter of flowmeter and 2 times of nominal diameter at downstream shall be clean，without any obvious indent，scale and peeling.

2　Where the upstream straight pipe section is not long enough，the stabilizer may be installed.

3　When installing，the center line of flowmeter shall be kept in line with that of pipeline，and the maximum deviation angle shall not be larger than 3°.

4　As for electromagnetic flowmeter，the fluid，flange and meter shell shall be ensured with the same potential，and the grounding shall meet the requirements of product's technical document.

3.4.22　As for the mass flowmeter sensor installed in pipeline，its flow direction mark shall be consistent with the flow direction of medium，the installation environment shall avoid vibration；when both ends of the sensor joint are fixed，the sensor shall be ensured not being stressed.

3.4.23　For the flow measuring of large scale flue and air duct，the multi-point sampling mode should be adopted and then the averaging should be implemented on the same cross section.