Variable Area Flow Meter

A variable area flow meter measures the volume flow of liquids or gases. The medium flows from bottom to top through a conical tube in which a so-called rotor moves. The position of the rotor indicates the flow rate. More Info

A variable area flow meter consists of a conical measuring tube and a ball or cylindrical body (floating body). When flow occurs, the floating body rises until the buoyancy and weight of the floating body are balanced by the force generated by the flow (it “floats”). The position of the float is a measure of the flow rate, which can be read on a scale attached to the measuring tube. More Info

Variable area flow meters are simple in design, require no external power source, have low maintenance costs, are inexpensive, and cause low pressure loss in the pipe. They are also robust and reliable. More Info

They are dependent on the density, viscosity, temperature, and pressure of the medium, have a limited measuring range (e.g., approximately 1:10), usually have to be installed vertically (flow from bottom to top), and are not suitable for media containing solids or highly opaque liquids. More Info

The measurement of flow in a conical pipe with a variable area was first mentioned by the American Edmund A. Chameroy, who applied for a patent for his invention in 1868. Over the next 15 years, further patent applications were filed with design improvements. Karl Küppers (1874–1933) made a decisive discovery in Aachen in 1908. He found that a rotating floating body significantly improved the accuracy and reliability of the measurement. More Info

The measurement accuracy depends on the model, medium, and installation conditions. Manufacturers often specify ±2% of the final value under optimal conditions, sometimes more for low flow rates or unfavorable conditions. The calculation is performed in accordance with VDI/VDE 3513-2 and is specified as an error limit and linearity limit. More Info

When the measuring device is used in potentially explosive areas, such as in the chemical industry, in mining, or with gases that are flammable. In such cases, certified devices that comply with legal and safety requirements are necessary. More Info

Liquids and gases, preferably clear and without solids or highly foaming components. Typical media are water, air, oil/water mixtures, coolants, etc. Special variants can also handle aggressive media. More Info

Usually vertically, with the flow from bottom to top. Stable inlet conditions are important to ensure a clean flow profile. Some variants can also be used horizontally or in downpipes. More Info

The measuring range is the ratio between the smallest and largest safe and meaningful flow rates that the flow meter can measure. If the range is too low, it may be necessary to replace the meter several times or use additional devices. For variable area flow meters, the measuring range is usually 1:10 (1:12). More Info

These factors influence buoyancy and viscosity, thereby shifting the equilibrium position of the float. Therefore, when dimensioning and calibrating, it is important to consider whether the medium changes significantly or whether the operating conditions vary. More Info

Yes. Many modern models offer accessories such as limit contacts, electrical transmitters, mA outputs, HART, Profibus, etc., to integrate the measurement into automated systems. More Info

It is caused by the sudden opening or closing of a ball valve, solenoid valve, or other fast-closing shut-off valve. The inertia of the liquid in the pipe and the abrupt deceleration or acceleration of the liquid column can cause a significant increase in operating pressure within milliseconds. More Info

System-related factors, such as pulsating flow generated by peristaltic pumps, can cause the float to pulsate. In addition to these system-related pulsations, incorrectly dimensioned floating body flow meters can also cause what is known as compression pulsation. This occurs when the operating pressure is insufficient to overcome the counterpressure generated by the floating body, allowing the floating body to be lifted. More Info

There are a number of national and international manufacturers from whom you can purchase variable area flow meters. You can find an overview at: More Info