Propeller Pumps
Propeller pumps are used for low lift, high flow rate conditions. They come in two types, axial flow and mixed flow. The difference between the two is the type of impeller. The axial flow pump uses an impeller that looks like a common boat motor screw and is essentially a very low head pump. A single-stage propeller pump typically will lift water no more than 20 feet. By adding another stage, heads from 30 to 40 feet are obtainable. The mixed-flow pump uses either semi-open or closed impellers similar to turbine pumps.
In permanent installations, propeller pumps are mounted vertically as shown in Figure 9. For portable pumping platforms, they are mounted on trailers or they are mounted on pontoons for use as floating intakes. Portable propeller pumps are commonly mounted in almost horizontal positions (low angles) to allow them to pump into pipelines easily as well as to be backed into a water source. Portable propeller pumps are commonly powered by the power-take-off (PTO) on tractors. On many farms, propeller pumps are used to pump out waste storage lagoons.
Power requirements of the propeller pump increase directly with the TDH so adequate power must be provided to drive the pump at maximum lift. Propeller pumps are not suitable under conditions where it is necessary to throttle the discharge to reduce the flow rate. It is important to accurately determine the maximum TDH against which this type of pump will operate.
Propeller pumps are not suitable for suction lift. The impeller must be submerged and the pump operated at the proper submergence depth. The depth of submergence will vary according to various manufacturers recommendations, but generally, the greater the diameter of pump, the deeper the submergence. Following recommended submergence depths will ensure that the flow rate is not reduced due to vortices. Also, failure to observe required submergence depth may cause severe mechanical vibrations and rapid deterioration of the propeller blades.
