Variable area flow meters / rotameters are used for the continuous measurement and indication of volumetric flow rates of liquids and gases. The measurement principle is based on the variable area (float) method, where the flow force of the medium positions a freely moving float within a vertically mounted measuring tube.

1. Flow direction: The medium enters the bottom of the vertical measuring tube and flows upward.
2. Force equilibrium: The flow generates a lift force on the float, while gravity and frictional forces act in opposition. The float assumes a stable equilibrium position corresponding to the instantaneous flow rate.
3. Reading of flow: The float’s height in the measuring tube is directly proportional to the volumetric flow. Measurement can be read on a calibrated scale or optionally transmitted via electronic signal outputs (e.g., 4–20 mA, pulse, or digital interface).

This technology is characterized by its simple construction, high operational reliability, and low maintenance requirements. Variable area flow meters are a proven and widely used flow measurement solution in the process industry, chemical and petrochemical sectors, food and beverage processing, and pharmaceutical production.

• Cost-effective and with low operating costs. Designed for easy installation and minimal maintenance throughout their entire life cycle.
• Robust construction. Perfectly suited for demanding applications in mining, hydromechanics, and in the oil, gas, automotive and semiconductor industries.
• Reliable accuracy. An accuracy of ± 2% can be achieved.
• Flexible installation, direct reading. The flowmeters can be installed horizontally or vertically, with the scale in any position.
• Versatile. Various connections are available in aluminum, brass and stainless steel.
• No external power supply required. Variable area flowmeters do not require an external power source, making them particularly suitable for remote or locations that are difficult to reach.