The bypass flow meter operates on the differential-pressure method. A ring with an orifice plate is installed in the pipeline. The orifice plate causes constriction of the flow and effects a drop in pressure. This pressure drop is proportional to the square of the flow rate.
If the pressure tap upstream of the orifice plate is connected by a pipe to that downstream of the orifice plate, a partial flow will flow through that pipe. This partial flow is proportional to the flow rate in the main pipeline.
The partial flow can be turned on and off, as required, by installing two ball valves in the bypass line.
The low-cost device in PVC is frequently used in swimming-pool water technology. The device in PVDF is suitable for the flow measurement of aggressive media, e.g. in water treatment, while the stainless steel type is mainly used for flow measurement of air and gases. The measuring range extends from 0.02 – 0.16 m3/h to 300 – 1800 m3/h for H20, and from 0.15 m3/h – 1.5 to 1200 – 6000 m3/h for air at STP.