Rotameters, also referred to as variable area flow meters, are widely used to measure gas and liquid flow. The basic principle of rotameter design includes a float that rotates as it is pushed by the flow. The rotation speed of the float indicates the rate of the flow. With today’s new technology, the basic rotameter has evolved its capabilities to provide highly precise flow rate measurements and to withstand a variety of extreme temperature and pressure conditions.
How Rotameters Work
The main elements of a rotameter are its metering tube, float, scale, end fittings and housing. The metering tube is a tapered container that holds the float and the liquid. The float is the object that actually measures the flow rate by moving with changes in the flow. The scale shows the flow rate measurements with marked unit increments. Fluid lines are connected to the end fittings in order to direct the fluid through the meter. The housing contains the whole assembly, including additional connections or components that may be included with late-model rotameters. A rotameter that needs to measure several different liquids will typically have several different scales.
Advantages of Rotameters
There are several types of rotameters available on the market today. Choosing the best one for your operations depends on your type of industry. All types of variable area flow meters offer the advantages of cost-effective operation because they do not need an external power source. They are also highly reliable, with a low rate of variability in multiple measurements taken under identical conditions. Installing a rotameter is generally uncomplicated and the passage of the flow through the meter gets rid of debris and buildup, cutting down on the necessity for cleaning.
Most rotameters are purely mechanical and do not need additional electrical power. This increases their durability, as the lack of electrical components allows them to operate in extreme conditions. Meters come in several sizes and their housing is typically metal, glass or plastic. For a rotameter’s data to have value, it is important to know the baseline operating temperature, pressure, viscosity and flow rate range.
The main risks to flow meters stem from factors such as temperature, high pressures, chemical corrosion and potentially volatile materials. With today’s new advanced materials, rotameters boast increased durability and expanded applications.
What to Know
When deciding on which rotameter design will work best for you, consider variables including the temperature and chemical composition of the flow, as well as the type of data you need your meter to transmit. The density and viscosity of the substance you need to measure will also play a role in your selection of the most functional rotameter for your purposes.
Rotameter Applications and Design
One major application of variable area meters is the monitoring of extraction on off-shore platforms. Due to the extremely high pressures in this environment, the simplicity and durability of the rotameter’s structure make it optimal for uses such as controlling the injection of substances into the extraction fluid to prevent corrosion or freezing.
Many industries use rotating equipment of various sizes to transmit coolants, dry gas seals and lubricants. Transmitting rotameters allow for the uninterrupted monitoring that is necessary for the safety and efficiency of the operation of your machinery. In dry gas seal applications, operators prefer meter bodies made from glass or plastic. While in previous years, glass was prevalent because it was possible to see the float through it, metal and plastic meters have an external indicator that is connected through a magnetic coupling. This set-up allows for remote observation and automatic monitoring.
Another widespread application of rotameters is industrial process analyzers, which continuously sample the flow. Installing a variable area flow meter provides an early warning system for clogs in the flow, which are a systemic problem that can seriously disrupt the process if an insufficient amount of sample material comes through the analyzer. A rotameter monitors flow continuously and catches a drop immediately, notifying users of a potential clog and giving them the chance to clean it out before the flow is interrupted completely.
Low-temperature rotameters are designed for use with products like liquid natural gas. In particular, during storage or transportation the liquid gas can begin to turn back into vapor. In order to avoid excessive pressure, it is flared so as to turn it back into liquid form. Several meter makers produce specialized low-temperature variable area flow meters for use in these applications. The meters’ streamlined design and high level of durability enable them to perform reliably.
Indicator-only rotameters are still very common across the board. They have the advantage of an ultra-simple design that is easy to install and does not impede flow, along with a high level of durability and repeatability of results. Metal tubing is more durable, while glass can be indicated for specific applications such as dry gas seals.
Flow meter makers today also produce rotameters with additional features, including analog output transmitters and flow alarms. These often have metal housing to afford increased protection for the added components.
Another modern feature available for the latest rotameter models is an armored housing made of high-tech metals that can resist extreme temperature fluctuations, pressure fluctuations and even explosions. Armored flow meters are increasingly used in hazardous areas. Due to today’s capabilities for remote data transmission, such flow meters may now be used in areas that may be difficult to access visually.
When choosing your meter, in addition to knowing the parameters of the intended application, be sure to know the size of the pipe where you plan to install it. Although the size ranges for rotameters is fairly limited, many manufacturers also provide fittings for meters that will be used in large pipes.
With a variety of rotameter designs on the market today, it is important to choose the one that will deliver the results you need, with the durability and reliability you expect from this type of meter. A quality manufacturer will be able to offer you help and resources in determining which features will optimize your process, as well as the best materials and design for your meter. Knowing your operating parameters, as well as any special circumstances, will help you find the most effective rotameter for your operation.