The technology behind a variable area flowmeter (sometimes called a rotameter) is more than a century old. But it continues to offer a reliable way to measure the flow of liquids and gases (e.g. water, helium, oxygen, etc.). A wide range of industries, from mineral processing to waste water management, rely on flow measurement to streamline their operations.

This article will provide a brief, but thorough, guide to variable area flowmeters. We'll discuss the different types that are available and the components that comprise them. You'll also learn how flow meters work as well as some of their most common applications.


Types Of Variable Area Flowmeters

Rotameters come in a variety of configurations. Traditionally, most designs have been installed vertically. They rely on gravity to apply downward force upon a floating object - called a float - that sits within a metering tube (the individual components are discussed in more detail below).

Some flow meters can be installed horizontally. This design uses a spring-based mechanism that applies force upon the float. As a result, gravity is a non-issue.

Some variable area flowmeters can be read locally. The metering tubes are imprinted with markings that allow technicians to visually determine the float's height. Other meters are designed with metal tubes that lack such markings. They are read remotely via signals that are sent by transmitters housed inside the metering tubes.


Basic Components Of A Variable Area Flowmeter

A typical rotameter is constructed of 5 basic parts: the metering tube, a float, a readable scale, connectors at both ends, and the assembly's housing. The metering tube has a conical shape. It is tapered at one end and widens toward the other end. Depending on its design, it may be constructed of glass, metal, or plastic. Glass is common, but metal is preferred for applications involving high temperatures and pressures. Plastic is used less commonly because it is less durable, but offers a cost-effective alternative to glass and metal designs.

As noted above, the float is a small object that sits within the metering tube. It is symmetrical and constructed of a hard material, such as aluminum, rubber, stainless steel, or titanium. The float moves up or down in the tube - assuming a vertically installed variable flow meter - in accordance with the target medium's flow rate.

The rotameter's scale is mounted on the side of the tube. Engineers and technicians can read the scale locally to determine the height of the float. The float's height indicates the medium's flow rate.

The flowmeter's assembly is designed with fittings on both ends. The fittings allow the device to be easily installed into the fluid line. A "clean" connection on both ends is critical.

The rotameter's housing contains all of the components discussed above. It is normally constructed of some type of metal, such as stainless steel.


How Variable Area Flowmeters Work: An Overview

A flow meter measures the flow rate of a medium, indicating the rate by the position and movement of the float within the metering tube. While the medium's flow exerts upward pressure on the float, providing it buoyancy, gravity exerts downward pressure on it. As the flow increases, the float rises in the tube. Its position informs the observer of the flow rate at the time of observation. Its movement - up or down - informs the observer of whether that rate is rising or falling.

Any change in the medium's flow rate triggers an immediate response from the float. That is, the float is a real-time indicator. If a state of equilibrium is desired, any such changes would presumably indicate problems that warrant attention.


Common Uses Of Variable Area Flowmeters

Variable area flowmeters are used in a wide range of different industries. Companies that employ them rely heavily on efficient flows to maintain a safe environment, reduce costs, and meet various performance objectives.

For example, flowmeters are used in offshore drilling to help maintain the form and integrity of select fluids. They're found in boiler rooms where they to provide data needed to regulate the flow of gases. Rotameters are used in the pharmaceutical industry to inform the removal of minerals from various cleaning solutions. The devices are employed in every industry where optimizing flow rates is important.

If flow rates affect your company's performance, your company likely already uses one or more different types of variable area flowmeters. Explore our product catalogue to find a design that accommodates your company's defined objectives.