Probably this is the most versatile pump of all. Impeller mechanisms are the basis
of thousands of types of pumps. 
The number of blades can vary from 1 to 10 or more. They operate over a wide speed
range -- from less than 30 to more than 3000 RPM.
Impeller pumps are excellent for moving impure liquids since they do not clog
very easily. For very impure liquids such as sludge, a single blade is sometimes
used.
Impeller pumps range in diameter from less than a quarter inch to 10 feet or more.
Sometimes they have diffusers to increase efficiency.
Sometimes the output of one impeller is fed directly into another impeller to
increase the head. As many as six or ten might be linked together, or connected
in two facing sets to double the output and even the pressures on the shaft and
pump casing.
(This is a 27-frame
animation, converted to animated GIF format and then super-compressed for Internet
transmission. (Note: On some Internet browsers it may be displayed much less smoothly
than the CD-ROM version, where the frames are timed to a thousandth of a second.))
