Understanding Positive Displacement Flow Meters: A Comprehensive Guide


Accurate liquid flow measurement is crucial for various industries, enabling precise control of processes, efficient resource allocation, and reliable operation. A positive displacement flow meter, or pd meter, is vital in achieving this accuracy by providing highly precise and repeatable measurements. These meters are designed to accurately measure the volume of fluid flowing through a system, making them suitable for a wide range of applications, from low flows to high viscosities.

Positive displacement flowmeters are a type of flow meter that operates by trapping and measuring discrete volumes of fluid. They offer exceptional accuracy, even in challenging flow conditions, and are known for their reliability and versatility. Positive displacement flow meters are available in various designs, such as gear meters, oval gear flow meters, nutating disk meters, and piston meters, each with unique working principles and advantages.

Positive displacement flowmeters have significant importance across multiple industries. Oil and gas are used for precise custody transfer, well production measurement, and process monitoring. In chemical processing, positive displacement flow meters ensure accurate dosing and blending of chemicals. Food and beverage industries rely on these meters for precise filling, batching, and dispensing. Pharmaceutical and biotechnology sectors use positive displacement flow meters for accurate dosage and process control. The versatility and reliability of positive displacement flow meters make them valuable for ensuring accurate flow measurement across a wide range of fluid types and applications in different industries.

How Positive Displacement Flow Meters Work

Positive Displacement Flowmeter Technology

A positive displacement flow meter (PD meter) is an instrument used to measure the flow rate of fluids by trapping and measuring discrete volumes of fluid as it passes through the meter. The meter’s internal components, such as gears, helical rotors, nutating disks, or pistons, create a chamber that fills and empties each fluid volume, providing accurate and reliable flow readings. As the fluid flows through the chamber, the internal components rotate or move, measuring the volume of fluid displaced. This rotation or movement is directly proportional to the flow rate, allowing the flow meter to calculate and accurately measure the fluid flow rate by counting and averaging the rotations or movements over time.

Positive Displacement Meter Types

  1. Oval Gear Positive Displacement Meters: These meters utilize two interlocking oval gears to measure liquid flow. The fluid enters the chamber between the gears, causing them to rotate and displacing a fixed fluid volume with each revolution.
  2. Helical Gear Flow Meters: HelixGear meters employ helical rotors with a unique twisted shape. As the fluid passes through the rotor chambers, it causes the rotors to rotate, measuring the flow based on the volume of fluid displaced.Helix Flow Meters
  3. Nutating Disk Positive Displacement Flow Meters: Nutating disk meters feature a disk that wobbles or nutates within a spherical chamber. The disk nutates as the liquid flows into the chamber, creating a measuring action that quantifies the volume of fluid passing through.
  4. Piston Flow Meters: Piston meters consist of a cylindrical chamber with a piston that moves back and forth as fluid enters. The piston’s movement displaces a fixed fluid volume with each stroke, allowing for accurate flow measurement.
Photo Courtesy of Omega Engineering

Advantages and Applications of Positive Displacement Flow Meters

High Accuracy and Precision for Reliable Flow Measurement

The positive displacement flowmeter offers exceptional accuracy and precision in flow measurement. Their displacement-based measurement mechanism ensures reliable and repeatable readings, making them ideal for applications that require precise flow control and accurate volume measurement. Some offer incredible linearity of ±0.075% and repeatability of 0.02%.

Suitable for a Wide Range of Fluids and Viscosities

Positive displacement flowmeters are highly versatile and can handle various fluids, including viscous liquids. Whether measuring low flow rates or high-viscosity fluids, positive displacement meters can provide accurate and reliable readings, making them suitable for various industries and applications.

Various Applications

Positive displacement flowmeters play a critical role in the oil and gas industry, providing accurate measurement for marketing terminals, refined product pipelines, crude oil transfer, feedstock import measurement, renewable fuels blending, aviation refueling, bunkering, and offloading.

The Best PD Meter In The Industry – Brodie International’s BiRotor Plus Meter

Brodie BiRotor Plus Positive Displacement Meter

The Brodie BiRotor Plus Meter stands out as the best positive displacement (pd) meter on the market. Its advanced design and superior performance set a new standard for accuracy, reliability, and versatility. The BiRotor Plus Meter incorporates cutting-edge technology and engineering innovations, ensuring precise flow measurement even in challenging conditions. Its double-case design combines rugged durability, improved accuracy, and reliable pulse output. The meter’s helical rotors eliminate the possibility of buildup, offering low maintenance requirements and extended service life. With a wide range of available sizes and pressure ratings, the BiRotor Plus Meter caters to diverse industry needs. It is the go-to choice for optimizing flow measurement in petroleum, industrial, and other relevant sectors.

Key Considerations for Positive Displacement Flow Meters

Fluid Viscosity and Temperature Range on Meter Selection

When selecting a pd flow meter, it is crucial to consider the viscosity and temperature range of the fluid being measured. Different flow meters are designed to handle specific viscosities and temperature ranges effectively. Understanding the fluid’s characteristics ensures the appropriate meter is selected to maintain accurate flow measurement.

Pressure Drop and Compatibility with System Requirements

Positive displacement flow meters can introduce a pressure drop in the system due to their design. Considering the pressure drop and ensuring compatibility with the system requirements is essential. Proper sizing and selection of the meter help minimize pressure drop while maintaining accurate flow measurement.

Maintenance and Calibration: Ensuring Optimal Performance

Regular maintenance and calibration are vital for the optimal performance of pd flowmeters. Following manufacturer guidelines for maintenance, such as cleaning and inspecting the meter to prevent clogging or damage. Additionally, periodic calibration ensures accurate measurement and reliable performance over time.

Factors Affecting Meter Accuracy and Longevity

Several factors can affect the accuracy and longevity of a positive displacement flowmeter. Understanding these factors allows for better management of the meter’s performance. Factors such as fluid composition, particulate matter, and system conditions can impact meter accuracy and longevity. Proper filtration, cleaning, and monitoring can help mitigate these factors and ensure the continued accuracy and longevity of the flowmeter.

Comparison with Other Flow Measurement Technologies

Positive Displacement Flow Meters vs. Turbine Flow Meters

Positive displacement and turbine flow meters are commonly used for flow measurement but differ in operating principles. Pd meters measure liquids flow by trapping and measuring discrete volumes, while turbine flow meters use a rotor with blades or vanes that rotate in response to fluid flow.

Positive Displacement Flow Meters vs. Magnetic Flow Meters

Positive displacement and magnetic flow meters are two distinct technologies employed for flow measurement. Positive displacement flow meters measure flow by displacing fluid tp calculate volumetric flow rate, whereas magnetic flow meters utilize electromagnetic principles to measure the velocity of conductive fluids. Magnetic flow meters are suitable for larger pipe sizes and can handle various liquids. In contrast, positive displacement flow meters accurately measure low to moderate flow rates and suit various fluid viscosities.

Positive Displacement Flow Meters vs. Coriolis Flow Meters

Positive displacement and Coriolis flow meters are highly accurate flow measurement technologies. Pd meters measure fluid flow by trapping and measuring volumetric flow, while Coriolis flow meters detect the deflection of liquids as it flows through vibrating tubes. Coriolis flow meters are known for their exceptional accuracy and suitability for various fluids. In contrast, the positive displacement flow meter offers advantages in lower pressure drop, suitability for viscous fluids, and the ability to handle a broader range of flow rates.

Maintenance and Troubleshooting Tips for Positive Displacement Flow Meters

Regular Inspection and Cleaning Procedures

Positive displacement flow meters require regular inspection and cleaning to maintain optimal performance. This includes checking for debris or buildup that may affect the meter’s accuracy or obstruct its moving parts. Following manufacturer guidelines, users should implement routine cleaning procedures. Regular inspection helps identify potential issues early on, ensuring the meter delivers accurate flow measurements.

Ensuring Proper Calibration and Accuracy

Calibration is crucial to maintaining accurate flow measurements with a positive displacement flowmeter. Regular calibration checks help verify the meter’s accuracy and make any necessary adjustments. Users should follow recommended calibration intervals and procedures outlined by the manufacturer. Users can maintain reliable and precise flow measurements over time by ensuring proper calibration.


In conclusion, pd flow meters are highly accurate and versatile instruments crucial in achieving precise and reliable flow measurements. Their unique working principles and design variations, such as gear meters, oval gear flow meters, nutating disk meters, and piston meters, offer exceptional accuracy and repeatability across various industries. These meters are suitable for measuring a wide range of fluids, including viscous liquids, and can handle different flow rates effectively. Proper consideration of fluid viscosity, temperature range, pressure drop, and regular maintenance is essential for optimizing their performance. With their ability to deliver precise and reliable measurements, positive displacement flow meters are invaluable in achieving efficient and optimized processes in industries such as oil and gas, chemical processing, and more.

Are you interested in learning more about Cherokee Measurement & Control’s exceptional PD flow meter offerings? Take the next step towards optimizing your flow measurement processes. Contact us today!