How to analyze and address common faults in metal tube float flowmeters

Thread Content

This post was last edited by yuchenchf on 2017-5-2 at 14:10. The metal tube float flow meter is a type of variable-area flow measurement instrument commonly used in industrial automation process control. It features a small size, a large detection range, and easy use. It can be used to measure the flow rate of liquids, gases, and vapors, and is particularly suitable for measuring the flow rate of media with low velocities and small flow volumes. During use, problems such as inaccurate indications often occur. The following is a brief analysis of how to resolve these not-so-complicated faults: Specific issue 1: The actual flow rate does not match the indicated value. Cause of the fault: Corrosion leads to changes in the float’s flow rate, volume, and maximum diameter ； Solution for changes in the inner diameter of tapered tubes: use a corrosion-resistant material. If the float size remains the same as before the replacement, it can be converted or recalibrated using the new weight and density ； If the dimensions are also different, it must be recalibrated. If the cylindrical surface of the float’s maximum diameter becomes worn and rough, affecting the measurement values, replace it with a new rotor. Floats made of or lined with engineering plastics may experience swelling, as well as changes in maximum diameter and volume; it is necessary to use floats made of appropriate materials.

Specific phenomenon 2: The actual flow rate does not match the indicated value.
Cause of the problem: Deposits such as scale or other contaminants on the float and conical tube.
Solution: Clean the components to prevent damage to the inner surface of the conical tube and the cylindrical surface of the float, while maintaining the original surface roughness.

Specific phenomenon 3: The actual flow rate does not match the indicated value.
Cause of the problem: Changes in temperature and pressure of gases, steam, or compressible fluids.
Solution: Make corrections based on the new conditions.

Specific phenomenon 4: The actual flow rate does not match the indicated value.
Cause of the problem: Fluid pulsations or sudden changes in gas pressure, leading to fluctuations in the indicated value.
Solution: Install a buffer tank or use instruments with damping mechanisms.

Specific phenomenon 5: The actual flow rate does not match the indicated value.
Cause of the problem: Bubbles in the liquid or liquid droplets in the gas.
Solution: Remove the bubbles or liquid droplets.

Specific phenomenon 6: The actual flow rate does not match the indicated value.
Cause of the problem: Gas gets trapped in the dead corners inside the instrument when it is used for liquids, affecting the buoyancy of the float.
Solution: Remove the gas, especially in cases of low flow rates where this issue is more pronounced.

Specific phenomenon 7: The flow rate changes, but the float or pointer moves slowly.
Cause of the problem: Particles or other contaminants between the float and the guide shaft, or bending of the guide shaft.
Solution: Disassemble and clean the components, remove any contaminants or deposits, and straighten the guide shaft. Bending of the guide shaft is often caused by rapid opening and closing of solenoid valves, which causes the float to rise suddenly; changing the operating mode can help resolve this issue.

Specific phenomenon 8: The flow rate changes, but the float or pointer moves slowly.
Cause of the problem: Iron powder or particles accumulate around the magnet in the magnetic coupling float assembly, causing the linkage or pointer to get stuck.
Solution: Disassemble and clean the components; during the initial operation phase, use a bypass pipe to thoroughly clean the pipes. A moving linkage with a manual and magnetic coupling connected to a filter is installed in front of the gauge, and there are adjustment points for stuck sections. Check whether there are any foreign objects between the rotating shaft and the bearings that could hinder movement; remove them or replace the relevant parts. Specific symptom 9: Flow rate changes, resulting in slow movement of the float or pointer. Cause of the fault: The engineering plastic float and the plastic-lined conical tube swell, or get stuck due to thermal expansion. Solution: Replace the parts with materials resistant to corrosion. For media at higher temperatures, avoid using plastic as much as possible and opt for parts made of corrosion-resistant metals. Specific symptom 10: The float or pointer moves slowly in response to changes in flow rate. Cause of the fault: A decrease in the magnetism of the magnets used for magnetic coupling. Solution: Remove the instrument and move the float up and down by hand to ensure that the pointer and other indicating elements move smoothly accordingly ； If it does not follow or follows unstably, replace the part or re-magnetize it. To prevent a decrease in magnetism, it is prohibited for the two coupling components to collide with each other