Flow Meter Types & Their Functions

Welcome to the Blue-White guide to flow meters and their functions. Flow meters are devices used to measure the flow of fluids, such as fuel, water, and other liquids. They are essential for many industries and applications, including industrial process control, medical diagnostics, and energy management. This guide will provide an overview of the different types of flow meters available from Blue-White and information on how to use and maintain them properly.

Flow Meter

A flow meter is a device used to measure the flow rate or quantity of a gas or liquid moving through a pipe. Flow meters measure the volumetric or mass flow rate of a liquid or gas. They are used to measure how much of a substance passes through a pipe over a period of time. Flow meters can measure flow in many applications, including water, oil, fuel, air, and steam.

They have applications in many industries, including water treatment, heating and air conditioning, industrial manufacturing, process control, and waste management.

For Starters, What is Flow?

Flow is a term used to describe the movement of materials or energy from one place to another in a continuous and organized manner. This can refer to the flow of fluids such as water, gas, and oil. Flow is an important concept in engineering and manufacturing in understanding how systems and processes work.

In this case, we will refer to flow as it applies to fluids in pipes. And in this application, flow is typically divided into two types: Open channel flow and closed conduit flow.

Open Channel Flow

Open channels are streams with an exposed surface and unrestricted access to the atmosphere. For example, canals and pipelines that are not completely full, such as drains and sewers.

In open channel flow, gravity is responsible for the motion of the liquid. The water level will gradually decrease down the stream as the flow progresses.

Closed Conduit Flow

Closed conduit flow is the flow of a liquid or gas through a pipe, channel, or another closed vessel. Closed conduit flow typically occurs at a constant velocity and depends on factors such as the pressure difference between the ends of the conduit and its length.

Water supply and district heating pipes are common places to observe closed conduit flow. Even drinking straws are a simple but efficient example of this. The flow rate here is largely determined by the pressure difference between the two ends, the distance between them, and the area of the conduit. Additionally, the hydraulics of the pipeline – such as its shape, roughness, and bends – also have an impact. All these factors come together to create the rate of flow.

Ranges of Flow Pressure

Flow pressure measures how much force is needed to move a liquid or gas through a system. It is measured in pounds per square inch (PSI) or kilopascals (KPa). The flow pressure range can vary greatly depending on the type of system, the size of the pipes, and the type of liquid or gas being pumped. For example, a residential water system typically operates at a much lower flow pressure than an industrial system. Flow pressure can also be increased or decreased by changing the size of the pipes, the number of fittings, and the type of pump.

Ranges of Temperature

Any flow will also have a temperature, with the typical range in most industries where they are used being from -40°F to +400°F (-40°C to +204°C). And to measure this, flow meters are designed to measure the flow rate in fluids with a wide range of viscosities, temperatures, and pressures. Flow meters can also detect changes in flow rates and can be used to detect leaks or other irregularities in the system.

Another term is thermal flow measurement, which reads how much heat is transferred while a gas passes a surface. The two main measurements taken with regard to temperature are simple readings via a temperature sensor and a heated flow sensor that measures the heat transfer from the flow of any given material inside the system.

What Does a Flow Meter Do?

As mentioned above, a flow meter is an instrument used to measure the flow rate of liquid or gas. It measures the flow rate by detecting and monitoring changes in pressure, level, or another variable caused by fluid passage through pipes.

Types of Flow Meters and Their Functions

Flow meters measure fluids, but fluids can be any liquid, viscous, or gas known to us. Hence, a wide range of flow meters is available on the market. All of these types vary in function and application.

Differential Pressure Flow Meters

Differential pressure flow meters employ the Bernoulli Equation, which states that a fluid’s pressure decreases while its speed increases. These types of flow meters report the difference between the two measurements. The first measurement causes a shift in kinetic energy when the air is forced through a hole in the flow meter, which is then measured by the second element.

The sub-types of differential pressure flow meters are rotameters / variable area flow meters, orifice plates, venturi flow meters, and pitot tube flow meters. These meters measure the pressure difference between two points, allowing for a precise calculation of the fluid flow rate.

Rotameters / Variable Area

A variable area flow meter is a differential pressure flow meter. Variable area flow meters are simple, versatile, and cost-effective devices that operate at a relatively constant pressure drop and measure liquids, gases, and steam flow. The variable area flow meter is popular for industrial and commercial flow indication because it has a linear scale, a relatively long measurement range, and a low-pressure drop – plus, they are simple to install and maintain.

Orifice Flow Meter

The orifice plate flow meter is a differential pressure flow meter used in clean liquid, gas, and stream mass flow measurements. It is available for a wide range of pipe sizes and allows for measuring fluid flows in larger pipes (over 6″ in diameter).

Venturi Flow Meter

Venturi flow meters allow the fluid to flow through a constricted section of pipe called a throat, where a pressure difference is created. The liquid speeds up and creates a pressure differential as it passes through, which is then used to calculate the volumetric flow rate of the fluid. Venturi meters are often used in applications requiring high precision levels with large volumes of liquid at low-pressure drops. They’re also suitable for liquids with a high solids content. Additionally, they are relatively easy to install because they have no moving parts. They can be fitted via flanged, welded, or threaded-end fittings, making them a popular choice for many applications.

Pitot Tube Flow Meter

Pitot tube flow meters are a common and cost-effective tool for measuring fluid flow rate in a pipe or duct. The pitot tube is inserted into the pipe to measure the difference in pressure between the upstream and downstream of the flowing fluid.

The installation process for a pitot tube is relatively straightforward, as it typically involves drilling a hole into a pipe and inserting the pitot tube into the fluid path with its impact port facing directly into the fluid flow.

Pitot tube flow meters remain attractive for many applications due to their low cost and easy installation process. They’re frequently used in HVAC and commercial aquatics systems, for example. Moreover, they offer minimal pressure drop, meaning they do not significantly impede the flow rate of the fluid.

Positive Displacement Flow Meter

A Positive Displacement Flow Meter is a device that measures the flow rate of a fluid by measuring the amount of fluid that is displaced by a series of chambers or rotors. This type of flow meter is highly accurate, durable, and efficient and is commonly used in industries such as oil and gas, food and beverage, and chemical processing.

PD or Positive Displacement flowmeters utilize a rotating mechanism within a precision-engineered chamber to capture fluid pockets, like filling a beaker with liquid and pouring it down an aisle, counting each fill.

• Reciprocating Piston Meter:

A reciprocating piston meter is a positive displacement flow meter that measures the volumetric flow rate of liquids and gases. It consists of a chamber with a piston, an inlet and an outlet valve, and a pressure transducer. The piston is driven by an external power source, such as an electric motor, magnetic field, or pneumatic cylinder, and moves back and forth in the chamber. As the piston moves, it displaces a fixed volume of liquid or gas, and the flow rate is calculated based on the speed of the piston and the volume displaced. The inlet and outlet valves open and close to control the flow rate, and the pressure transducer measures the pressure inside the chamber.

• Oval-Gear Meter:

An oval-gear meter is a positive displacement flow meter that measures fluid or gas flow through two oval-shaped gears with close-fitting teeth. The gears are connected to each other and are placed in a chamber that has a known volume. As the fluid or gas passes through the chamber, the gears rotate, and the volume of the chamber is displaced. The displacement of the volume is measured, and the flow rate of the fluid or gas is calculated.

• Nutating-Disk Meter:

A nutating-disk flow meter works by passing fluid through a disk that is mounted on a shaft, which is connected to a motor. The disk is free to rotate around the shaft as the fluid passes through, causing the disk to rotate, or nutate, at a rate proportional to the flow rate. The rate of rotation and nutation is then measured and converted into a flow rate.

• Rotary-Vane Meter:

A rotary-vane flow meter uses a rotary vane, a type of impeller, to create a pressure differential across the meter, which is then used to calculate the flow rate. The inner part of the rotary vane meter consists of several vanes, each connected to a central shaft. As the fluid passes through the meter, the vanes rotate, causing a series of gears to turn. The gears are connected to a mechanical counter that records the total flow rate. The rotary vane meter is highly accurate and reliable, often used in the automotive industry to measure fuel and oil flow rates. The rotary vane meter is also used in medical applications, such as anesthetic delivery systems. The design of the rotary vane meter allows it to be used in a wide range of temperatures and pressure ranges.

Volumetric Flow Meter

Volumetric flow meters measure the speed of the flow rather than the actual volumetric rate directly. The volumetric flow rate is calculated by multiplying the measured velocity by the cross-sectional area at which it’s installed, accurately representing how much material passes through in a given time period. Flow meter technology has become more advanced, with digital displays becoming more commonplace with improved accuracy due to better calibration technology and new sensing methods.

Ultrasonic Flow Meter

Ultrasonic flow meters measure flow rate by detecting fluctuations in ultrasonic oscillations. They come in two varieties: time difference and Doppler. Time difference type meters, also called time-of-travel meters or transit meters, measure the time taken for ultrasonic waves to travel from one point to another, while Doppler-type meters measure the frequency shift of soundwaves reflected from the moving particles in the medium. Both are used for accurate flow rate measurement.

Mass Flow Meter

Mass flow meters measure the mass of a material that passes through the system in a given period of time. They measure the mass per unit of time, typically expressed in kilograms per second (kg/s). Mass flow meters measure the speed and density of the material as it passes through the device. This data is then used to calculate the mass flow rate. Mass flow meters are typically used to measure the flow of liquids, gases, and solids in industrial processes, such as the chemical, food, and pharmaceutical industries. Coriolis flow meters are the most popular mass flow meters used in industries today.

Blue-White Flow Meters For Any System

Flow meters are an incredibly important and versatile tool for measuring the flow of liquids, gases, and solids in a variety of industries. There is an ideal meter for any application, from ultrasonic flow meters to variable area flow meters.

Blue-White has you covered when it comes to fluid control processes. We manufacture industrial-grade flow meters that are accurate and robust, so you can depend on them to keep your processes running smoothly, safely, and cost-effectively. From rotameters / variable area flow meters to paddlewheel flow meters to ultrasonic flow meters, all our products are Made in the USA and ready to ship! Get peace of mind by knowing your flow meters are reliable and of the highest quality. Trust Blue-White for all your flow meter needs.

Written by:
Blue-White® Industries
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