Rotameters also known as Variable Area Flow Meters are used to measure the volumtric flow rate of liquids or gases in a closed tube. They provide a constant flow rate measurement and can also offer optional switching capabilities to control the flow in a system or process. Most rotameter flow bodies are made of glass or plastic, some are metal. Acrylic and polyamide are common plastic types used in rotameter construction. Metal rotameters are generally made in stainless steel or brass bodies. Some is specifically designed for the measurement of low flows of liquid and gases.