Variable Area Flowmeters
Information about the Variable Area Flowmeters
Variable Area (VA) flow meters measure flow rate of a liquid or gas by relating linear displacement of an internal “float” or sharp-edged orifice plate to a corresponding flow rate. As flow rate increases, the orifice area that the flow moves through also increases – thus, the term Variable Area. Variable Area meters either allow flow through a peripheral orifice formed between a tapered wall and a float (normally, only installed vertically), or an annular orifice and an internal tapered metering pin, normally balanced by a spring, allowing any orientation. Flow rate is read on Variable Area meters by aligning the position of the piston/float to an adjacent calibrated scale.
Accuracies range from ±5% of full scale to ±2% depending on flow range, fluid and detection technique. Generally, turndown is unlikely to exceed 5:1 and they will be susceptible to viscosity and fluid density changes. Most will require a clear fluid. They benefit from not requiring power and that they can be made from economic materials.