the correct selection of the installation site and the correct installation of the flowmeter are very important links, if the installation of errors in the light will affect the measurement accuracy, the heavy will affect the service life of the flowmeter, and even damage the flowmeter. The length of the front and rear straight pipe sections required by different flow meters is different.
The general requirements for the upstream and downstream straight pipe sections of flowmeter in the Code for Construction and Acceptance of Automation Instrument Engineering-GB50093-2013 1. are as follows:
Mass flow meter --- No requirement;
rotameter --- upstream is not less than 0~5 times of pipe diameter, downstream is not required;
target flowmeter-upstream is not less than 5 times of pipe diameter, downstream is not less than 3 times of pipe diameter;
turbine flowmeter-upstream is not less than 5~20 times of pipe diameter, downstream is not less than 3~10 times of pipe diameter;
vortex flowmeter-upstream is not less than 10~40 times the pipe diameter, downstream is not less than 5 times the pipe diameter;
electromagnetic flowmeter-upstream is not less than 5~10 times the pipe diameter, downstream is not less than 0~5 times the pipe diameter;
Ultrasonic flowmeter-upstream is not less than 10~50 times the pipe diameter, downstream is not less than 5 times the pipe diameter;
Volumeter --- No requirement;
orifice plate-upstream is not less than 5~80 times of pipe diameter, downstream is not less than 2~8 times of pipe diameter;
nozzle-upstream is not less than 5~80 times of pipe diameter, downstream is not less than 4 times of pipe diameter;
Venturi pipe, elbow pipe and wedge pipe-the upstream shall not be less than 5~30 times the pipe diameter, and the downstream shall not be less than 4 times the pipe diameter;
Velocimeter pipe-upstream is not less than 3~25 times the pipe diameter, downstream is not less than 2~4 times the pipe diameter.
2. flow meters
1. If there is a 90 elbow or a downward joint upstream of the flowmeter installation point, the upstream of the flowmeter shall have an equal diameter straight pipe section of not less than 20D, and the downstream shall have an equal diameter straight pipe section of not less than 5D.
2. If the upstream of the flowmeter installation point has a 90 elbow in the same plane, the upstream of the flowmeter shall have an equal straight pipe section of not less than 25D, and the downstream shall have an equal straight pipe section of not less than 5D.
3. If there is a tapered pipe upstream of the flowmeter installation point, the upstream of the flowmeter shall have an equal diameter straight pipe section of not less than 15D, and the downstream shall have an equal diameter straight pipe section of not less than 5D.
4. If there is a divergent pipe upstream of the flowmeter installation point, the upstream of the flowmeter shall have an equal straight pipe section of not less than 18D, and the downstream shall have an equal straight pipe section of not less than 5D.
3. special attention:
1. Vortex flowmeterinstallation point, the continuous opening and closing of the valve will have a great impact on the service life of the flowmeter, and it is easy to cause permanent damage to the flowmeter.
2. Avoid installing the flowmeter on overhead and long pipelines as far as possible, because the sagging of the flowmeter is very easy to cause the sealing leakage between the flowmeter and the flange. If it is necessary to install it, the pipeline fastening device must be set at the upstream and downstream 2D of the flowmeter.
3. The installation of mass flowmeter has no special requirements for the front and rear straight pipe sections. But the following conditions must be met:(1) For liquid media, the flowmeter should be at the low point of the pipeline. Avoid vaporization of the medium due to low back pressure and affect the measurement results. For gaseous media, the flowmeter cannot be located at a local low point in the pipeline to avoid liquid accumulation in the measuring tube and causing measurement errors. 2) For liquid media, it must be ensured that the media fills the pipeline during operation. No gas-liquid or liquid-solid two-phase fluid can exist in the measuring tube. If installed on a vertical pipe, the fluid should flow from bottom to top. If flow from top to bottom is necessary, a restriction orifice plate can be placed behind the flow meter to prevent the measuring tube from being evacuated. (3) The flowmeter and the connecting flange must be completely aligned, otherwise it will bring external stress to the measuring tube and affect the measurement results. (4) To avoid interference caused by strong electromagnetic fields on the flowmeter, there should be no interference sources such as large motors near the flowmeter. (5) The vibration frequency shall be staggered when the mass flow meters of the same type are installed adjacent to each other to avoid the negative impact of resonance, and the distance between the two flow meters shall be at least 4 times the length of the meter. (6) Pay attention to the natural vibration frequency of the flowmeter phase measurement and the natural vibration frequency of the pipeline, otherwise it will cause measurement fluctuations. (7) Stop valves should be installed before and after the flowmeter to facilitate zero correction before operation.
4. The rotameter must be installed on a vertical pipe with the medium flowing from bottom to top and without vibration. During installation, it shall be ensured that there shall be a straight pipe section not less than 5 times the inner diameter of the pipe and not less than 300mm before the flowmeter; 5. When the measured medium contains suspended solids, the target flowmeter shall be installed horizontally. When the target flowmeter is installed on the vertical pipeline, the liquid flow direction should be from bottom to top. The length of the straight pipe section before the end of the target flowmeter shall not be less than 5 times the inner diameter of the pipe, and the length of the straight pipe section after the outlet end shall not be less than 3 times the inner diameter of the pipe.