In terms of technology and application, propeller meters are fairly similar to turbine meters. The rotating element and its suspension in the fluid stream are the fundamental differences between the two. A propeller is usually composed of thick injection molded plastic and is supported by a single bearing assembly. It faces straight into the flow. Turbine blades are typically narrower and supported on both sides by two lighter-weight bearing assemblies.
Propeller flow meters revolve a “pinwheel” (rotor) in the flow stream using the mechanical energy of the fluid. The rotor’s blades are oriented in order to convert energy from the flow stream into rotational energy. Bearings support the rotor shaft. The rotor spins faster in proportion to the speed of the fluid.
Shaft rotation can be detected mechanically or by seeing the blades move. Magnetic detection of blade movement is common, with each blade or implanted piece of metal generating a pulse. To circumvent the material and construction limits that would occur if wetted sensors were utilized, propeller flow meter sensors are normally situated outside of the running stream. As the fluid flows faster, more pulses are created. The pulse signal is processed by the transmitter to determine the fluid flow. In both the forward and reverse flow directions, transmitters and sensing systems are available.
Propeller meters are precise and reasonably inexpensive, making them cost-effective even when only used for a short period of time. Propeller meters are commonly employed in agricultural and turf, as well as municipal water, but they can also be found in industrial settings.