Flowmeters

Variable area flow meters, often referred to as “rotameters,” 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 as in the traditional rotameter, or an annular orifice and an internal tapered metering pin in the Lake Monitor. The attributes of the Lake Variable Area flow meter are a linear relationship between flow rate, pressure differential and piston displacement. Flow rate is read on Variable Area meters by aligning the position of the piston/float to an adjacent calibrated scale.

Positive Displacement (PD) flow meters are volumetric flow measurement instruments ideal for low flow rates, highly viscous fluids, and measurement of flows involving starts and stops or pulsing. Positive displacement flow meters are similar in design to the gear pump.  The principle of operation is reversed however; instead of the gears driving the fluid, the fluid drives the gears.  A non-intrusive hall-effect sensor detects the movement of the gear and as each gear tooth passes the sensor, a square wave pulse is produced and a discrete volume of liquid is measured. The resulting pulse train is proportional to the actual flow rate and provides a highly accurate representation of the fluid flow.

Differential pressure flow meter models have directly connected, large-throated, non-clogging flow nozzles. The flow nozzle design is a long life, wear-resistant element that provides many years of service. Differential pressure flow meters are known worldwide as the rugged, “install them and forget them” type of flow meters.