Flow meters are essential in a number of industrial applications like water treatment facilities. Although there are many technically advanced flow meters available today, some still prefer simple instruments such as variable area flow meters. This type of flow meter is reliable and robust and also more economical than high-tech options.
Variable area flow meters have been around for over a century. They have become more affordable over the years, and when the application calls for a flow meter that is not only flexible but also cheaper, variable flow meters become the go-to solution. Aside from water treatment plants, a variable flow meter can be applied in the following:
- Water filtration systems
- Commercial aquariums
- Chemical processing plants and laboratories
- Pollution monitoring
- Crop irrigation systems
- Nutrient feed systems
One specific example of variable area flow meter application is in reverse osmosis systems as a measuring tool for the output and reject. These meters are critical in ensuring system efficiency. Reverse osmosis filtration systems benefit significantly from variable area flow meters because they can measure the actual flow of fluid where the pressure drops as the filter saturates. Flow meter operators can quickly check if the filters require replacement by monitoring pressure drop.
How does a variable flow meter work?
A variable area flow meter uses a tapered tube for measuring fluid flow. The fluid passes through the smaller end up to the larger end of the tapered tube. The movement of the fluid forces an indicator to move up. As the indicator or float approaches the top of the meter, the space between the tube and float also increases. The larger the area, the more fluid required to push the float higher. Changing the taper angle of the tube, the length of the tube, and float mass results in different flow range calibrations.
Importance of accuracy and repeatability of measurement
Understanding the importance of accuracy and repeatability affect the selection process of variable area flow meters. If you don’t know the precise accuracy and repeatability requirements of the intended application, there is a tendency to buy a flow meter not suited for expected use. Manufacturers may term the accuracy of a flow meter generally, hence it is necessary to learn the intricacies of the term to find the right flow meter.
On the other hand, repeatability is the capability of the flow meter to reproduce flow rate measurements consistently while subject to the same working conditions. In some applications such as in processing plants, repeatability is often more important than accuracy.
Different types of flow meters
Aside from variable area flow meters, there are different types of flow meters used today including mass flow meters, ultrasonic flow meters, and positive displacement flow meters. There is really no such thing as a universal flow meter compatible with all types of applications. To qualify a flow meter is suitable for a use, you must consider how adequately it will perform under such circumstances without costing too much for installation and maintenance.