The propeller rotates on a horizontal axle which drives the volume and flow rate indicator. The propeller shaft usually rotates on a minimum of two bearings. The bearings and shafts are made of stainless steel or an equivalent noncorrosive material. The drive assembly can be either direct or magnetic. The magnetic drive provides for a fixed seal in the housing between the propeller and the indicating head.
Direct drives use a packing-type seal.
The propeller measures the velocity of the water in the pipeline or meter section. Therefore, when ordering a saddle-type meter, the pipe I.D. must be specified. Some companies use a correction factor to account for various I.D.'s rather than changing gears. This should be checked when buying the meter. A recommended practice is to buy the meter already installed in a pipe section complete with straightening vanes.