Primary Functions And Usage of Liquid Flow Meters

A liquid flow meter gauges fluid flow in volume, mass—Linear, and nonlinear. You get the flow rate by gauging the fluid velocity. The type of fluid and application advice on the type of liquid flow metering you should apply. 

Paddlewheel Sensor

This is the most common flow meter. It is cost-effective and easy to use; You use it to gauge water-like fluids’ flow rate. Thus, you cannot use it on gases and slurry fluids. You buy a paddlewheel sensor alongside flow fitting and insertion.
If your paddlewheel sensor is a turbine meter, you will buy it with a straight inlet pipe of 10 pipe diameter. The outlet pipe should be five pipes in diameter. You fit the rotor of the sensor perpendicular to the flow direction. Thus, it makes limited contact with the flowing fluid cross-section. 

Positive Displacement (PD) Flow Meter

In the practical world, you can get a flow fitting with no adequate straight pipes. That is where you need a PD flow meter. They are also useful with slurry fluids. 
PD meters work by holding a known amount of fluid and then releasing it. This principle ensures that the meter has minimal interruptions caused by bends, vents, and channel diameter changes. 

There are several types of PD meters, as we will see below.


They have gears that rotate as the fluid passes through the meter. Gear meters are of several subtypes. Each subtype derives its name from the shape of the gear.

Oscillating Piston

The meter is also known as a reciprocating piston. Each piston fills a cylinder and empties it in oscillations; Each stroke carries a limited and known liquid quantity.

Oval Gear

Oval gear works as a combination of gear meter and oscillating meter. It has the shape of two gears put together. As the liquid passes through the meter, it pushes the gear making it rotate. It passes a known amount of fluid with each oscillation. Since they are two gears, it ensures that there is a continuous flow of fluid. 

Helical Gear

The gear has a shape of a helix. It is spiral and works on the principle of gear meters. 

Rotary Vane

These meters have rotating impellers with two or more vanes. The areas between the vanes have distinct sizes. Thus, they pass a known amount of fluid with each rotation. 

Magnetic Flow Meters

These are non-mechanical flow meters. They have no moving parts. Thus, they are suitable for slurry and dirty liquids. They are also perfect for conductive fluids. These types of meters have a display, which is a vital part of the meter. You can use the display for remote monitoring and data logging. 
They use the Faraday law of Electromagnetic induction. The liquid creates a voltage as it passes through a magnetic fluid; It produces more voltage as more fluid passes in a short time.

How a Magnetic Flowmeter Works

As we have seen, it applies the Faraday law of electromagnetic induction. It creates a magnetic field and channels it to the fluid running through the liquid flow metering. When the fluid passes the magnetic fluid, it creates a voltage. The voltage increases with the increasing speed of the fluid. 
Please do not turn a magnetic flow meter near its electric conductive limit. It suits off once it surpasses the limit. Be keen on the working conditions and changing production. The two can change the electrical conductivity of a fluid. 

Generally, a magnetic flow meter has the highest speed of 2 or 3 meters per second. The difference in pressure and processes may limit the use of the meter. 

Ultrasonic Flow Meter

These meters work with slurry, wastewater, and other dirty fluids. They fill in the gap on the types of fluids that damage the conventional fluid flow metering. Also, the meters act on a principle of a shifting signal. The signal moves with gas bubbles or suspended particles. That’s why you can’t use the meter with clean fluids. The signal principle is known as a doppler effect.
Ultrasonic water flow meters use ultrasound to send signals. The signal travels through the fluid. Then the meter tracks the movement of the signal. The speed of the signal determines the volumetric flow rate of the fluid. 

How Ultrasonic Flow Meter Works

The meter uses sound waves to track down the volumetric speed of a fluid. It is the best meter to use with highly viscous fluids. It is also effective in corrosive fluids since it is non-intrusive. 
The frequency of the sound signal reflects the same throughout the fluid when the fluid is at rest. When the fluid is in motion, the reflection of the signal changes; The Doppler effect causes the change. 

The meters are useful in fluids that can absorb the ultrasound. Also, the meter should determine the fluid flow under the doppler effect. 


Liquid flow metering is important. You should know what your firm needs. Check the condition of your fluid and select the best liquid flow meter to suit your needs.