Key Points for Selecting Vortex Flow Meters

In the field of fluid control, vortex flow meters are widely favored due to their broad applicability in measuring gases, liquids, and steam. However, choosing the right vortex flow meter is a complex process that involves considerations of flow range, pipe diameter, measurement accuracy, medium characteristics, and more.

1. Medium Applicability Range

Vortex flow meters are generally applicable to gases, liquids, and steam. Nevertheless, there are some media that are not suitable for measurement with vortex flow meters. Fluids containing a large amount of solid particles or suspended matter are not suitable. Some media with extremely high kinematic viscosity under working conditions, such as heavy oils, are also not suitable. Additionally, when the measured medium is steam, it is necessary to specify whether it is saturated steam or superheated steam.

2. Flow Range

The commonly used flow should be controlled in the upper middle part of the measurable range of the vortex flow meter. Since the measurement of the lower limit flow of the vortex flow meter is easily affected by pipe vibration, it is advisable to avoid measuring near the lower limit as much as possible. When the flow range exceeds the measurable range of the vortex flow meter, methods such as reducing or expanding the diameter can be adopted. However, it should be noted that the diameter reduction or expansion of the meter should not be too large. When the diameter is reduced, the flow velocity increases, resulting in increased resistance and back pressure. When the diameter is expanded, cavitation is likely to occur. Under the condition of allowing the straight pipe section, it is recommended to choose "reducer + straight pipe section" to ensure the stable measurement of the fluid.

For example, the measurable range of liquid and gas for different pipe diameters is shown in the following table:

Vortex flow meters are not suitable for measuring pulsating flow. When there are power mechanical equipment such as Roots blowers, reciprocating pumps, and plunger pumps in the pipeline system, strong pulsation will be generated. If the pulsation frequency is within the vortex frequency band, measurement errors will occur, and in severe cases, the Karman vortex street may not even be formed.

3. Pipe Diameter and Measurement Accuracy

Vortex flow meters can be installed in a pipeline type or an insertion type according to different installation methods. For the pipeline type, the minimum pipe diameter is usually DN15, and the maximum can generally reach DN300. If a larger diameter is required, the insertion type can be selected, and the maximum diameter of the conventional range can reach DN2000.

The accuracy of vortex flow meters also has several levels and is classified according to the measured medium. For pipeline-type vortex flow meters, the measurement accuracy can reach 1.5% when measuring liquids and 1.0% when measuring gases. For insertion-type vortex flow meters, the accuracy can reach 1.5% and 2.5%.

4. Medium Temperature and Nominal Pressure

Generally, it is divided into three ranges: normal temperature, medium temperature, and high temperature. The temperature ranges are -40 - 100°C (normal temperature), -40 - 250°C (medium temperature), and -40 - 350°C (high temperature). If the on-site medium temperature is higher, it is necessary to negotiate the order.

The nominal pressure is mainly classified according to the installation method. The main types on the market are flange clamping type (2.5MPa), flange connection type (10MPa), and insertion type installation type (1.6MPa).

5. Power Supply and Output Signal

Power Supply

According to the current market demand, the main power supply types include +12VDC (three-wire pulse output), +24VDC (three-wire pulse output type and two-wire current output type), 3.6V lithium battery, and dual power supply.

Output Signal

According to the current market demand, the main output signals include voltage-frequency pulse output, two-wire 4 - 20mA output, HART output, and modbus RS485 communication. Generally, current output and frequency pulse output are standard configurations, while HART and modbus are optional.

6. Installation Environment

When the flow meter is installed in a good indoor environment and there is no need for signal remote transmission, only the flow value needs to be read on site, and the installation position of the flow meter is convenient for operation and data reading, a battery-powered type can be selected. When the installation environment of the flow meter is poor, or the installation position is not convenient for on-site reading of the flow value, or in the case of centralized management, a split type can be selected.

7. Temperature and Pressure Compensation

Whether vortex flow meters need temperature and pressure compensation depends on the actual needs. If the working conditions have little deviation or the requirements are not high, temperature and pressure compensation is not necessary. If accurate measurement is required, compensation is needed. Vortex flow meters can be equipped with built-in temperature and pressure sensors, and the intelligent meter head can perform compensation calculations.

When measuring general gases, both temperature and pressure need to be compensated simultaneously because the volume flow of gases changes when the temperature or pressure changes. When measuring superheated steam, both temperature and pressure need to be compensated simultaneously because the density of steam changes when the temperature or pressure changes, and the mass flow also changes accordingly. When measuring saturated steam, either single temperature compensation or single pressure compensation is required. There is a fixed correspondence between the density of saturated steam and the temperature or pressure. Knowing either one can determine the density of saturated steam.

8. Protection Level

Common IP protection levels of vortex flow meters include IP65, IP67, IP68, etc. The appropriate IP protection level should be selected according to the installation position of the vortex flow meter. When installed indoors and in general outdoor environments, IP65 is sufficient. When installed in a pipeline well that is generally not easy to accumulate water, an IP67 or higher protection level should be selected. When installed in a pipeline well or ditch that is easy to accumulate water, an IP68 split type should be selected to prevent the sensor from being damaged by rainwater immersion.

In conclusion, when selecting a vortex flow meter, it is necessary to comprehensively consider the above factors to ensure that the selected flow meter can accurately measure the flow of the medium under specific working conditions and meet the actual needs of the project.