Rotameters, as flow measurement instruments, are essential for various applications where on-site flow indication or remote alarm and measurement are required. This article outlines the selection criteria for different types of rotameters, detailing the considerations to ensure optimal performance and reliability.
1. General Guidelines for Selecting Rotameters
When choosing a rotameter for applications involving small measurement ranges and moderate accuracy requirements, consider the following:
Diameter and Pressure Class: The suitable nominal diameter (DN) should range from DN15 to DN150. For lined pipes, DN20 to DN150 is preferred. The pressure rating should typically be PN10, PN20, or PN50.
Accuracy: For local indication, an accuracy level not lower than 2.0 should be selected. For remote transmission, ensure the rotameter has an accuracy of at least 1.5.
Flow Range Utilization: The standard operational flow should be within 60% to 80% of the rotameter’s full scale. Ensure that the process’ minimum and maximum flow rates are between 10% and 90% of the full scale.
Material Considerations: The body material of the rotameter must match or exceed the quality of the pipeline material. The float material should not be lower than 316 stainless steel (SS). For corrosive media, consider materials like Monel, Hastelloy, or specific high-grade alloys.
Magnetic Filtration: When the process medium contains small amounts of ferromagnetic particles, install a magnetic filter upstream of the rotameter.
Damping Mechanism: For gas, steam, or pulsating fluid measurements, rotameters should be equipped with a damping mechanism.
Installation Orientation: Rotameters should be installed vertically, with fluid flowing from bottom to top.
2. Selection of Glass Tube Rotameters
Glass tube rotameters are commonly used for measuring small flow rates of clean gases and liquids. Here are key selection criteria:
Application Suitability: Glass tube rotameters are ideal for clean air, inert gases, and water. The maximum operating pressure should be less than 415 kPa (gauge), and the highest operating temperature should not exceed 90°C.
Safety and Limitations: Avoid using glass tube rotameters with flammable, explosive, toxic, contaminated, or corrosive fluids.
Pressure Rating: The typical pressure rating for glass tube rotameters is PN10.
3. Selection of Metal Tube Rotameters
Metal tube rotameters are robust and suitable for a wider range of applications, including hazardous and corrosive environments:
Application Suitability: They are appropriate for flammable, toxic, or corrosive fluids as long as the medium does not contain ferromagnetic, fibrous, or abrasive particles.
Lining Options: For highly corrosive media, the conical tube can be lined with PTFE or PFA. Ensure that the lining material matches the pipeline’s internal lining specifications.
4. Selection of Jacketed Metal Tube Rotameters
Jacketed metal tube rotameters are used for fluids that may solidify, crystallize, or vaporize under certain conditions:
Heating or Cooling: The jacket should be supplied with an appropriate heating or cooling medium.
Diameter Limitation: The maximum nominal diameter for jacketed rotameters is typically DN80.
5. Selection of Purge Rotameters
Purge rotameters are designed for specialized applications requiring flow control during processes such as level, pressure, or differential pressure measurement:
Integrated Systems: Purge rotameters should be equipped with a flow control needle valve and a pressure/flow stabilizing device.
Size Limitation: The maximum diameter for purge rotameters is typically DN250.
Conclusion
Choosing the right rotameter involves understanding the specific needs of your application, including fluid type, flow range, pressure, and environmental conditions. By following these detailed guidelines, you can ensure that your selected rotameter delivers accurate and reliable performance tailored to your industrial requirements.