Liquid Flow Meters: A Comprehensive Guide


Liquid flow meters are devices used to measure the volumetric or mass flow rate of liquids. They have a wide range of applications across many industries including water treatment, food and beverage, pharmaceuticals, chemicals, oil and gas, and more. This article provides a detailed overview of the different types of liquid flow meters, their working principles, applications, advantages and limitations.

What is a Liquid Flow Meter?

A liquid flow meter is an instrument used to measure the volumetric flow rate of a liquid flowing through a closed conduit. It works by sensing the flow using different techniques, displaying the measured flow rate and total accumulated flow in an integral or remote-mounted display, and generating an output signal that is proportional to the flow rate. The flow rate data is essential for monitoring, controlling and optimizing processes that involve liquid flow.

Some key terms related to liquid flow meters:

  • Flow rate – Volume of liquid passing per unit time, measured in units like liters/second, gallons/minute, etc.
  • Accuracy – How close the measured flow rate is to the actual value. Higher accuracy meters have lower errors.
  • Repeatability – Ability of the meter to provide consistent results every time the same flow rate is measured.
  • Turndown ratio – The ratio between the maximum and minimum flow rates that can be measured by a flow meter. A high turndown ratio allows greater flow measurement rangeability.

Types of Liquid Flow Meters

There are several different technologies and working principles used in liquid flow meters. The most common types are:

1. Differential Pressure Flow Meters

These meters work by measuring the pressure difference across a primary device like an orifice plate, Venturi tube, flow nozzle or pitot tube placed in the flow. The primary device creates a constriction that produces a pressure drop proportional to the flow rate. This differential pressure is sensed by the instrument.

Advantages: Simple, low cost, high turndown ratio, suitable for dirty liquids

Applications: Water, chemicals, oil

2. Positive Displacement Flow Meters

These meters contain moving components that repeatedly fill and displace a known volume of liquid. Counting the number of fill/displace cycles per unit time determines the flow rate.


  • Nutating disc
  • Oval gear
  • Rotary piston
  • Diaphragm

Advantages: High accuracy, suitable for high viscosity liquids

Applications: Flow calibration, custody transfer, food and beverage

3. Velocity Flow Meters

These meters have sensors that measure the liquid’s velocity. The velocity is then converted into a flow rate using the pipe cross-section area.


  • Turbine
  • Electromagnetic
  • Ultrasonic
  • Vortex

Advantages: No pressure loss, high rangeability

Applications: Water, chemicals, hydrocarbons

4. Mass Flow Meters

These meters directly measure the mass flow rate instead of volumetric flow rate. They work by sensing the force produced by the flowing liquid with a sensor inserted in the flow.


  • Coriolis
  • Thermal

Advantages: Measure mass flow directly, high accuracy

Applications: Custody transfer, filling applications

5. Variable Area Flow Meters

These simple meters have a tapered tube and float/piston assembly. Liquid flow raises the float, with its height indicating flow rate on a scale.

Advantages: Simple, low cost, transparent operation

Applications: Low flow measurement, flow control

Key Considerations for Selecting a Liquid Flow Meter

To choose the optimal flow meter for an application, the following parameters must be considered:

  • Liquid properties – density, viscosity, temperature, conductivity, impurities
  • Pipe size
  • Flow rate range – minimum and maximum
  • Operating pressure and temperature
  • Accuracy required
  • Straight inlet/outlet piping requirements
  • Installation constraints – weight, space
  • Cost

Additionally, the meter must be compatible with the liquid. Factors like corrosion resistance, materials of construction and pressure drop must be accounted for.

Applications of Liquid Flow Meters

Liquid flow meters are ubiquitous across industries like:

Final Words

Accurate liquid flow measurement is critical across many different industries and applications. Various types of flow meters based on different working principles are available to measure flow rate, velocity, and even mass flow.

The choice of flow meter depends on the liquid properties, pipe size, flow rates, pressure and temperatures as well as the desired accuracy. Each technology has its own advantages and limitations that must be analyzed before selecting the optimal flow meter for an application. Proper installation and maintenance are also key to sustaining flow meter performance.

Meet the Author

Riaz Danish

Riaz Danish is SmartMeasurement’s President and CEO. He has diverse experience in the flow measurement industry spanning over 40 years, including overseeing sales, marketing, and manufacturing major initiatives on a global scale. Riaz has used his vast knowledge of the flow meter and pressure measurement industry to found SmartMeasurement. He has developed and grown the organization over the last 20 years. Riaz has focused on developing and implementing a supply chain management portal for flow measurement with E-commerce for the major markets in US/Canada, Europe, and Asia, as well as implemented and managed a global network of distributors and third-party vendors. He holds a Bachelor of Science in Mechanical Engineering (BSME) from San Diego State University and a Master’s in Business Administration-International Marketing from San Francisco State University.

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