The PD Meter Working Principle Explained

Discover the working principle, and features of Positive Displacement (PD) meters, an essential device that can be used to measure liquid flow across multiple sectors, from aviation to the marine realm. 


Over the years, ISOIL engineers have been studying the PD meters’ working principle and possible applications, gaining in-depth knowledge and experience of their various intricacies. As a result, we have a broad range of models to choose from in order to cater to the different needs of an increasingly demanding market.


On this page, you will find out more about:




What Is A PD Meter?


A Positive Displacement (PD) meter is largely used to measure liquid flow accurately


PD meters work on the principle similar to the concept of repeatedly filling a beaker with any fluid and then pouring it downstream while keeping count of the number of the times the beaker is filled so as to determine its volume. This is the only device that measures the volume of the liquid passing through it directly without using any external power.


In order to determine volume, small pockets of the fluid are trapped within a high-precision chamber between the rotating components. The rotational velocity of the rotor is directly proportional to the fluid flow rate because it is the flow of fluid which is causing the rotation in the flow meter.


PD meters operational value is unrivaled in industries such as Oil & Gas, aviation, and marine applications. PD meters are especially useful in situations where fluid measurement needs to be highly precise. Their robustness and intrinsic reliability as well as their capacity to work with different viscosities makes them ideal for dispensing fuels.



Understanding PD Meters And Their Different Working Principles


There are several models of PD meters with a series of mechanical differences that need to be addressed in order to have a comprehensive overview of this tool functioning. 



Rotary PD Meters


This type of device employs gears or rotors with vane blades to generate a motion. Each rotation represents a precise and known volume. It is by counting these rotations that accurate flow measurement is obtained. This tool is especially useful to manage viscous fluids and high flow rates. 



Single and Double Case Meters


Single-case meters are suitable for industrial applications, whereas double-case meters are largely used for high-pressure applications like in pipelines. This is because the double-case design helps in pressure balancing of the liquid inside the PD meter.  



Gravity Meters


This PD meter operates using a working principle that does not require external power. In fact, their calculation depends on the natural flow of the fluid, which is influenced by gravity



Pump Gravity Meters


Combining the working principle of gravity meters with an additional pump mechanism, these devices can measure fluid flow both for gravity unloading and to perform operations when a pump is required


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What Are The Main Advantages Of Using A PD Meter?


The PD meter working principle is becoming an increasingly preferred choice for fluid measurement


Here, you can find the main advantages of using a PD meter.


  • High-precision: as the fluid passes through them, it is easier to assess the volume. 


  • Viscosity handling: these instruments can deal with different liquids and viscosities without recalibration.


  • Design: PD meters do not need straight pipes upstream and downstream for accurate measurement. Therefore they can fit in places where space is narrow or limited.


  • Durability: they can work in harsh environments where there is the presence of corrosive substances, high pressures, and extreme temperatures. 


  • Consistent performance:  the PD meter working principle is not sensitive to the flow profile and vibrations. 


  • Maintenance: thanks to their design, these devices are easy to clean and maintain. 


Would you like to know more about ISOIL PD meters’ working principle and the different models we can offer? 


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