Axial flow pumps are a type of centrifugal pumps. They push liquids, gases, and liquids carrying solids, through pipes. These generators of pressure keep fluid flowing through the pipes by the use of rotating impellers, like fans or propeller blades. Axial flow pumps are used in systems with low head, or pressure drop, that requires greater flow rates than can be attained with passive distribution methods. There are various kinds of axial flow pumps, which depend on the type of pumping system required for distribution of the fluid medium.
The impellers of axial flow pumps can be attached in line with a sealed motor, or the motor can sit on the outside of an elbow of the pipe. The pitch of impeller blades of an axial flow pump can be adjusted to different angles toward or away from the direction of flow. The greater the angle of the impeller blades, the greater the pressure drop added and the greater the flow rate produced. The ability to change the angle of impeller blades allows axial flow pumps to work under low-flow/high pressure or high-flow/low pressure conditions.
The advantage of axial flow pumps over passive fluid distribution is that their use in areas like rises or corners. In such locations flow tends to slow down and suspended material gets dropped. Axial flow pumps can speed up the flow to increase the carrying capacity of the fluid medium. Powered by electric motors or internal combustion engines, these pumps can be used as centrifugal sewage pumps where the rotating impeller acts as both a separator and grinder. In these systems, sewage can be rerouted or ground into smaller particles, allowing remaining debris to stay in suspension where it is lifted and carried in a direction parallel to the pump shaft.
Another popular application for in-line axial flow pumps is a ballasting system in which the conducted medium is the ballast of a sailboat. Docked without crew or cargo, the mast or sails of a boat may be buffeted by the wind. As the boat leans to one side, fluid in one ballast tank is pumped through a pipe to another reservoir on the other side of the craft in order to maintain balance. This must be done in response to rapid changes in the attitude of the craft. For that an online axial pump is added to the line and can change its motion, clockwise or counterclockwise, and speed, depending on where and how fast the ballast fluid needs to move.