A variable area flow meter operates on mechanical principles. Their construction is simple yet durable, making them suitable for a variety of applications. The basic operational principle is that changes in flow rate can be observed and measured as the flow displaces a piston, float or vane until it reaches a steady state. As the liquid or gas passes thorough the housing tube, the movement of the measuring part indicates rate. This type of meter can be placed almost anywhere along the pipe and does not require complicated maintenance routines. It is also highly versatile and can be used to measure flow rates of liquids, gases and steam.
Generally, flow rate meters measure the volume or mass of gas or liquid that is displaced during a specific period of time, for example, liters per second. Density is an important factor in determining rate.