Engineering Intro

The Different Flow Meter Types You Need To Know

Flow is categorized or branded into closed conduit flow and open channel flow. Closed conduit flow takes place when the flow is generated or prompted by a pressure difference in the pipe. For example, flow in district heating pipes or water supply pipes.

Additionally, the flow rate largely relies on the pressure difference the hydraulic properties of the pipe (restrictions, roughness, and shape), the area of the tube, the distance between the ends, and the pressure difference between the ends. On the other hand, open channel flow takes place when the flowing stream has an unconstrained or free surface unenclosed to the atmosphere. Typical examples are flows in the vented pipelines or canals. From these categories, there are plenty of flow meter types to choose from. For a little help, here are a few that you should know. Read on!

Turbine Flow Meter

There are a lot of designs for manufacturability of turbine flow meters. However, generally, they’re all founded or established on the same plain principle. When a fluid flows through a conduit and responds on the broad blade of a turbine, then the turbine will start spinning and rotating.

The spin rate is gauged to measure the flow. For this type of flow meter, the turndown ratios might be at least 100:1, mainly if the turbine flow meter is carefully assessed for a single fluid and leveraged at continuous conditions. Precision might be better than positive or negative 0 to 1 percent.

Differential Pressure Flow Meter

In this flow meter type, the flow is measured by calculating or computing the pressure drop over a barrier thrust in the stream. The DP flow meter device has the Bernoulli Equation as a basis for its operating principle. The further calculated signal and pressure drop is a function of the, by and large, square flow speed.

Generally known types of DP flow meter devices are Rotameters, Venturi Tubes, Flow Nozzles, and Orifice Plates.

Venturi Tube

Because of the dependability and simplicity, the Venturi tube flow meter is usually applied in applications where it is required to have lower pressure drops and higher turndown ratios. In this flowmeter type, the flow rate of the fluid is calculated by minimizing the cross-sectional flow area in the pipe.

Thus, it causes a pressure difference. Once it passes the constricted area, the fluid will flow through a recovery exit area. At least 80 percent of the differential pressure produced at the cross-sectional flow area in the flow path is recovered.


The rotameter or variable area flow meter comprises of a vertically designed plastic or glass tube with a massive end at the top. Plus, a metering float which can freely move within the vessel. The flow of the fluid makes the float to rise within the tunnel. It is because the buoyancy and upward DP of the fluid surpasses the impact of gravity.

The metering float goes up until the circular or ring-shaped area between the tube and metering float increases significantly. Thus, enabling a state of balance between the buoyancy and differential pressure factors, as well as the downward gravity factors.

The metering float’s height is a sign of the flow rate. The rotameter can be graduated or calibrated in the right flow units.

Electromagnetic Flow Meter

This type of flow meter is based on Faraday’s law of electromagnetic induction. In Faraday’s law, it states that an electromotive force will be generated when a lightning rod goes through a magnetic field.

Additionally, the fluid acts as the conductor or lightning rod. Moreover, the magnetic field is generated by coils outside the flow indicator. The electromotive force produced is, for the most part, equivalent to the flow rate.

The electrodes installed in the wall pipe perceives the voltage, which is calculated by a secondary element. This flow meter type can gauge corrosive and difficult slurries and liquids. Plus, they can assess flow in upward and downward directions with uniform accuracy. Take note that electromagnetic meters can only measure electrical conductive liquids.

Thermal Flow Meter

This type of flow meter functions independent of viscosity, pressure, and density. Thermal flow meters utilize a heated sensing element separate from the path of the fluid flow. The heat conducted is equal to the mass flow rate. Plus, the temp difference is measured to mass flow.

The precision of this flow meter type relies on the viscosity of the fluid, heat capacity, flow rate, pressure, temperature, and the reliability of the actual process.


When choosing a flow meter device, it’s important to note some factors. These are lifetime, maintenance, operating requirements, head loss, flow rate range, legal constraints, cost, and accuracy. These critical factors are, more often than not, related to one another. Take the list of flow meter types to guide you.

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