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Positive Displacement Flow Meter: Definition, Functions and Applications

Positive Displacement (PD) Flow Meter is one type of flow meter. It is a volumetric flow measuring instrument which measures flow by passing the correct volume of liquid in each revolution. PD Flow Meter is a device whose internal drive components are hydraulically locked together with the fluid volume.

This tool belongs to the type of flow meter that has high accuracy (± 0.1%) and a good repeatability rate (0.05%). Based on its components, the PD flow meter does not require a power supply for its operation. In addition, this flow meter also does not require a straight pipe from upstream to downstream for installation.

PD flow meters are not affected by the viscosity, density or turbulence of the fluid in the pipe. This makes it ideal for measuring the flow of liquids with high viscosity, such as oil, fuels and solvents which are difficult to measure with other types of flow meters. Based on the domain of use, the PD flow meter is most widely used as a household water meter. While in the industrial and petrochemical fields, this tool is usually used for liquid and gas batch filling.


How do PD Flow Meters Work?

All PD Flow meters operate by passing an isolated volume of fluid through a series of gears or chambers within the meter. So by measuring the volume of isolated fluid that passes through this tool, the calculation data will be obtained. Each design of the PD flow meter uses a different way to isolate and calculate this volume.

PD meters are available in sizes 1/4 inch to 12 inch and can operate with turndowns as high as 100:1 although ranges of 15:1 or lower are much more common. In using this type of flow meter, the liquid to be measured must be clean and free of contaminants (particles). Particles larger than 100 microns must be removed by a filtering method. So for this reason, PD meters are generally not recommended for measuring types of fluids or fluids that are abrasive/corrosive.

PD Flow Meter Parts

In general, the components or parts of a PD meter consist of filters, filters, air discharge assemblies, dampeners, temperature compensation systems and various types of valves. Of course, these parts have their respective functions. Where the continuity of the function of each existing part makes this type of flow meter work optimally.

Advantages in Use

Below are some of the advantages or pluses offered by positive displacement flow meters. Such as:


One of the main benefits of using a PD flow meter is the high level of accuracy it offers. The high precision of the internal components means that surface clearances are kept to a minimum. The smaller this clearance is, the higher the accuracy is related to how high the accuracy is.


Range and Repeatability

Another advantage of this flow meter is a high level of capability. Where this tool can be used in types of fluids with high viscosity. In addition, as previously explained, this tool has a high level of repeatability.



One of the main points in choosing the type of flow meter is reliability. Where reliability is related to the expectation of using the tool to work optimally for many years. But unfortunately, some types of flow meters sometimes require servicing or recalibration after continuous use. PD flow meters offer other advantages, namely having a high level of reliability. This is of course when compared to other types of flow meters.


Easy maintenance (low maintenance)

Because it has a high level of reliability, this PD meter also tends to be easy to maintain. So that if one day it is damaged or needs to be re-calibrated, it will not be too difficult.

Limitations in Use

Limitations in a flow meter tool certainly go hand in hand with its advantages. The PD flow meter is no exception. The weakness of this tool is that because it has a very powerful flow sensor, of course there are limitations to its use.

First, this tool should not be used for liquids containing large particles. Unless the particles have been filtered before the liquid enters the measuring chamber. This tool is also not suitable for liquids that contain a lot of air bubbles. Another factor that becomes a limitation and requires consideration is the pressure drop caused by this PD meter.



Types of PD Flow Meter

There are several types or types of Positive Displacement Flow meters. Some of them consist of:


Liquid Control Flow Meter Distributor


Reciprocating or oscillating piston

In this type each piston is operated mechanically or magnetically to fill the cylinder with liquid. Each step taken represents a finite fluid measurement.


Gear Flow Meter

Gear flow meters rely on internal gears that rotate as fluid passes through them. There are 2 types of gear flow meters based on the shape of the internal components. The two consist of oval gear and helical gear.


Nutating Disk

In this type a disk is mounted on an axis and each rotation represents a finite amount of fluid displaced. This disc type flow meter has a circular disc mounted on a shaft. By tracking the movement of the shaft, the flow meter will determine how many times the chamber is filled with liquid. The results of this activity are used to determine the flow rate.

Rotary vane

In this type, using a propeller that rotates on an axis



In this type, the fluid is drawn to the inlet side of the oscillating diaphragm and then removed to the outlet. The oscillating cycle of this diaphragm is calculated to determine the flow rate.



One of the well-known and widely used PD flow meter brands in the industrial world is Liquid Controls. This product has been widely sold in various parts of the world because it has been tested for reliability and quality. PT. Badja Abadi, is the official distributor of Liquid Controls products in Indonesia, which is directly appointed by lcmeter America. Reporting from the official website, namely liquidcontrolsflowmeterindonesia.com, there are many types of PD flow meters that can be purchased.

Starting from the M, MA, MS and MSA series. Each series certainly has different specifications. In addition, each series is also available in various sizes. So you can determine the type of PD Flow meter that fits the required specifications. For those of you who are interested in buying, you can click on the Liquid Controls Indonesia website listed above.