How does a positive displacement flowmeter work?

Positive displacement flowmeters are a crucial category of flow measurement devices widely used across various industries. As a leading flowmeter supplier, we have in - depth knowledge and rich experience in these devices. In this blog, we will explore how positive displacement flowmeters work, their applications, advantages, and the different types available.

Working Principle of Positive Displacement Flowmeters

Positive displacement flowmeters operate on a simple yet effective principle. They measure the volume of fluid that passes through the meter by repeatedly trapping and releasing fixed volumes of the fluid. This is achieved through a mechanical process where the fluid forces moving components within the meter to rotate or reciprocate.

Let's break down the working process step - by - step. First, the fluid enters the flowmeter chamber. Inside this chamber, there are precisely designed measuring chambers or compartments. As the fluid flows in, it fills these chambers. Then, the moving parts of the flowmeter, such as rotors, pistons, or gears, are actuated by the pressure of the incoming fluid. These moving parts separate the fluid into distinct, known - volume segments.

As the moving parts continue to operate, they displace the trapped fluid from the inlet side of the chamber to the outlet side. Each time a fixed - volume chamber is filled and emptied, it represents a specific volume of fluid that has passed through the meter. A counting mechanism, often mechanical or electronic, keeps track of the number of these displacements. By multiplying the number of displacements by the volume of each chamber, the total volume of fluid that has flowed through the meter can be accurately determined.

Types of Positive Displacement Flowmeters

There are several types of positive displacement flowmeters, each with its unique design and application.

Gear Flowmeters

Gear flowmeters consist of two or more gears that mesh together inside a housing. As the fluid enters the meter, it causes the gears to rotate. The teeth of the gears create sealed chambers that trap the fluid. The rotation of the gears moves these chambers from the inlet to the outlet, displacing the fluid. Gear flowmeters are known for their high accuracy and are commonly used in applications where precise measurement of viscous fluids is required, such as in the oil and gas industry.

Nutating Disc Flowmeters

In a nutating disc flowmeter, a disc, which is mounted on a central pivot, nutates (tilts and rotates in a circular motion) as the fluid passes through the meter. The fluid enters the chamber and causes the disc to move in a specific motion. This motion creates separate volumes of fluid that are displaced from the inlet to the outlet. Nutating disc flowmeters are often used in residential and commercial water metering applications due to their simplicity and reliability.

Oval Gear Flowmeters

Oval gear flowmeters use two oval - shaped gears that rotate in opposite directions. The oval shape of the gears allows for a more efficient trapping and displacement of the fluid compared to regular circular gears. These flowmeters are suitable for measuring a wide range of fluids, including both low - and high - viscosity liquids, and are commonly used in chemical processing and fuel dispensing applications.

Applications of Positive Displacement Flowmeters

Positive displacement flowmeters have a wide range of applications across different industries.

Oil and Gas Industry

In the oil and gas sector, positive displacement flowmeters are used for measuring the flow of crude oil, refined petroleum products, and natural gas. They are essential for custody transfer applications, where accurate measurement of the volume of oil or gas being transferred between parties is crucial for financial transactions. For example, in a pipeline transporting crude oil from an oil field to a refinery, a positive displacement flowmeter can accurately measure the amount of oil being transferred, ensuring fair and accurate billing.

Chemical Industry

The chemical industry relies on positive displacement flowmeters to measure the flow of various chemicals, including acids, solvents, and polymers. These flowmeters can handle corrosive and viscous chemicals with high accuracy, making them suitable for processes such as chemical mixing, dosing, and batch processing. For instance, in a chemical manufacturing plant, a positive displacement flowmeter can be used to precisely measure the amount of a reactant being added to a chemical reaction vessel.

Food and Beverage Industry

In the food and beverage industry, positive displacement flowmeters are used to measure the flow of liquids such as milk, fruit juices, and beer. They are designed to meet strict hygiene standards and can provide accurate measurements even for viscous and particulate - containing fluids. For example, in a brewery, a positive displacement flowmeter can measure the amount of beer being filled into bottles or kegs, ensuring consistent product quality and accurate inventory management.

Advantages of Positive Displacement Flowmeters

Positive displacement flowmeters offer several advantages over other types of flowmeters.

High Accuracy

One of the main advantages of positive displacement flowmeters is their high accuracy. They can provide measurement accuracies of up to ±0.1% or better, depending on the type and design of the flowmeter. This makes them suitable for applications where precise flow measurement is critical, such as in custody transfer and high - precision chemical dosing.

Wide Viscosity Range

Positive displacement flowmeters can handle fluids with a wide range of viscosities, from very low - viscosity liquids like water to highly viscous fluids like heavy oils. This versatility makes them suitable for a variety of industries and applications.

Low Flow Sensitivity

These flowmeters can accurately measure low flow rates, even down to very small volumes. This is important in applications where precise measurement of small amounts of fluid is required, such as in laboratory settings or in the dosing of additives in manufacturing processes.

Comparison with Other Flowmeter Types

While positive displacement flowmeters have many advantages, it's also important to compare them with other types of flowmeters. For example, SLDF2000 Clamp - on Flow Meter is a non - intrusive flowmeter that can be easily installed on the outside of a pipe without the need to cut into the pipe. It uses ultrasonic technology to measure the flow of fluid. Unlike positive displacement flowmeters, which require the fluid to physically displace moving parts, clamp - on flowmeters measure the flow based on the transit time or Doppler effect of ultrasonic waves in the fluid.

Another type is the Thermal Mass Flow Transmitter. This flowmeter measures the mass flow rate of a gas by using the principle of heat transfer. It is commonly used in applications where the measurement of gas flow is required, such as in industrial combustion processes or environmental monitoring. Positive displacement flowmeters, on the other hand, are mainly used for liquid flow measurement, although some can also be used for gas flow measurement in certain applications.

The Insertion Type Electromagnetic Flow Meter measures the flow of conductive fluids based on Faraday's law of electromagnetic induction. It is suitable for large - diameter pipes and can provide accurate flow measurement for a wide range of conductive fluids. Positive displacement flowmeters, however, are more suitable for applications where high accuracy and the ability to handle viscous fluids are required.

Conclusion

Positive displacement flowmeters are a reliable and accurate solution for measuring the flow of fluids in a wide range of industries. Their unique working principle, high accuracy, and ability to handle a wide viscosity range make them a popular choice for many applications. Whether you are in the oil and gas, chemical, food and beverage, or any other industry that requires precise flow measurement, positive displacement flowmeters can provide the solution you need.

If you are interested in learning more about positive displacement flowmeters or other types of flowmeters we offer, we encourage you to contact us for a detailed discussion. Our team of experts is ready to assist you in selecting the right flowmeter for your specific application and to provide you with the best possible solution. We look forward to the opportunity to work with you and help you achieve accurate and reliable flow measurement in your operations.

References

1. "Flow Measurement Handbook: Industrial Designs and Applications" by Richard W. Miller
2. "Process Flow Measurement" by Robert W. Miller
3. Technical literature from various flowmeter manufacturers