A propeller is a high-speed axial flow impeller which is typically used for low viscosity liquids. Depending on the propeller diameter, the propeller speed varies from 400 rpm to 1800 rpm. The propeller size is usually limited to 450 mm for top-entry mixers. The propeller is generally operated to produce down pumping action directed towards the bottom of the vessel, until deflected by the floor or the wall of the vessel. Side entering propellers have diameters ranging from 250mm to 850mm.