Water meters vary in size, quality and design. Meter size should be determined by the size of the pipe, the range of flow to be measured, and the head loss characteristics. The manufacturer should provide this information in a manner similar to the chart on the next page. The meter must accommodate the expected range of flows, and the lowest anticipated flow should fit within the normal accuracy of the meter. It is also desirable to select a size that will not create excessive head loss.
Most meters use a magnetic drive between the propeller and the indicator head.
This eliminates problems with sealing direct drive bearings which sometimes bind because of sand or corrosion. Propeller size usually ranges from 50 to 80 percent of pipe diameter. Small propellers are suitable when there is little variation in the flow, but larger propellers generally are more accurate when there are wide fluctuations in flow. The larger propeller is driven by more of the total flow. Make sure the meter gear ratio is selected for the insid e diameter of the pipe in which the meter will be installed.