Turndown ratios allow for accuracy and flexibility when making flow measurements in industrial applications. Whether you are using a turbine flowmeter, Coriolis flowmeter, or another type of flowmeter, understanding Turndown ratios can help you make better decisions about equipment selection, performance optimization, and long-term operational efficiency.
What is Turndown Ratio?
“Turndown ratio” is a term commonly used in the engineering field, especially in the areas of flow control, heating or power output. It indicates the operational flexibility of a device over a range of maximum and minimum outputs. The following is a detailed explanation of turndown ratio:
Definition : The turndown ratio is the ratio between the maximum and minimum capacity of a piece of equipment (e.g. a boiler, flow meter or pump) and indicates whether the piece of equipment can still be operated efficiently at the lowest load. A higher turndown ratio means that the equipment can be operated at well below maximum load without loss of efficiency or stability.
Formula:
Example: If a boiler has a modulation ratio of 10:1, this means it can operate consistently at 10% of its maximum load without compromising performance.
Applications:
Boilers and burners: Higher turndown ratios allow boilers to operate more efficiently, adjusting to varying heat demands without frequent start-ups and stops.
Flow meters: Flow meters with higher turndown ratios can accurately measure high and low flow rates.
Pumps and compressors: Higher turndown ratios provide greater operational flexibility in processes that require variable flow rates.
Turndown Ratios for Different Flow Meters
| Flow Meter Type | Turndown Ratio | Applicable Fluids |
| Magnetic Flow Meter | 100:1 or higher | Conductive liquids (e.g., water, wastewater, acidic or alkaline liquids) |
| Coriolis Flow Meter | 100:1 or higher | Various liquids and gases |
| Orifice Flow Meter | 3:1 to 10:1 | Gases, liquids, steam |
| Ultrasonic Flow Meter | 20:1 to 100:1 | Various liquids, some models for gases |
| Vortex Flow Meter | 10:1 to 20:1 | Gases, liquids, steam |
| Positive Displacement Flow Meter | 10:1 to 50:1 | High-viscosity fluids (e.g., oils, lubricants) |
| Rotameter (Variable Area Flow Meter) | 10:1 to 12:1 | Various liquids and gases |
| Turbine Flow Meter | 10:1 to 20:1 | Clean liquids and gases |
How to Choose the Right Turndown Ratio?
When selecting a flow meter, it is important to match the turndown ratio to the specific needs of the application. Consider the following factors:
- Flow volatility: If your process involves significant flow fluctuations, choose a flowmeter with a high turndown ratio to ensure accurate measurements are maintained throughout the range.
- Accuracy requirements: If accurate measurements are required at both low and high flow rates, selecting a flowmeter with a higher turndown ratio can help maintain accuracy.
- Budget and operating costs: Although high turndown ratio flowmeters are typically more expensive, they can reduce the need for multiple flowmeters, thereby reducing costs in the long run.
- Fluid type and conditions: Some flowmeters are better suited to specific types of fluids (e.g., liquid vs. gas, clean vs. dirty). Choose a flow meter that matches the characteristics of the fluid, which will affect performance and the achievable turndown ratio.
Summary
Turndown ratio is a key factor in flow meter performance and efficiency. By understanding this concept, you can make better equipment selection decisions and ensure that your flow measurement system delivers accurate, reliable results across a wide range of flow conditions. Whether it’s optimizing process control, improving energy efficiency, or reducing equipment costs, the right turndown ratio can play an important role in achieving operational success.
Apure offers precision flow meters, as well as water quality monitoring analyzers, level measurement instruments, and temperature and pressure measurement instruments. Please contact us for more information.