The Basic Working Principle of Positive Displacement Flow Meter


Flow meters are utilized to measure totalized volumetric flow rates for fluids. There are several types of industrial flow meters available on the market, however, each of it has its own advantages and is specialized in its own area of use. The positive displacement, for that instance, is a mechanical meter best suited for non-corrosive, clean mediums. It is capable of measuring a wide range of fluids including those that contain high viscosities.

Define: Positive Displacement Flow Meters (PD)

These are colloquially also referred to as the workhorses in the flow measurement applications. It is a device that measures the flow rate of a fluid by allowing it move through the system in increments. They are highly capable of performing multiple intricate and vital flow measurements when implemented in industrial applications. Although, Positive displacement meters face a lot of competition from the advancing new-technology flow meters available on the market, they remain an effective solution for certain specific applications. Positive displacement (PD) are widely and mainly applied in billing applications for both, gas and liquids. They help to determine the amount of gas that is being used in various commercial offices, buildings, residences, and other massive industrial plants.

Principle of Working

This is the only flow measurement technology that directly measures the volume of the liquid or fluid passing through the meters. The action of fluid transfer is achieved by placing an oscillating, nutating, or rotating object in the fluid path so that it measures the exact quantity of the displacing fluid. One of the most popular nutating disc type flow meters in the industry technology is the Positive Displacement. These devices repeatedly entrap the fluid in the system in order to measure its overall flow. The entrapment is typically achieved by using rotating parts that constitute the moving seals between one another and/or the flow meter body. The rotation in the system can either be detected mechanically or by detecting the overall movement of a rotating part. However, it is naturally understood that if more fluid flows through the system, the rotating parts turn faster. Furthermore, a transmitter present in the meter processes the signal to determine the flow of the fluid.

Varying Designs in a Positive Displacement Flow Meter

Many PD meters are designed differently, wherein, the rotating parts consists of tight tolerances so that the seals can prevent the fluid from entering the meter before it is measured. Another design consists of bearings that help to support the rotating parts. Additionally, some displacement meters have output pulses that are often used by a secondary electronic instrument in order to determine the flow rate, whereas, some other meters have mechanical registers that display the overall flow on a local display.