Maximum pumping head

Some references on the web state that there is a limitation on the height that an Archimedes screw can pump water.

http://en.wikipedia.org/w/index.php?title=Archimedes%27_screw&oldid=36077659 Wikipedia entry which states


 * Since the primary objective in this case is to lift water to a given height rather than simply move it from a river to the irrigation field, more than one machine was used to successively lift the same water volume, due to the limitations of this machine.

That implies a height limitation, but the only limitation I see is that the water cannot be raised higher than the top of the screw.

See also Head (hydraulic), which states:


 * There are four types of head used to calculate the total head in and out of a pump:
 * Static head is due to gravitational force on a column of fluid.
 * Velocity head is due to the motion of a fluid.
 * Friction head is due to the frictional forces against a fluid's motion.
 * Pressure head is due to other mechanical forces acting on a fluid.

pump-zone.com article see page 2.


 * The only limitation of Archimedes screws is their low pumping head. Still, pumps lifting water as high as 36.5' have been installed.

www.pumpbiz.com definition of head not what I thought
 * Note!!! A pump does not create pressure, it only creates flow! Pressure is a measurement of the resistance to flow. In Newtonian fluids (non-viscous liquids like water or gasoline) we use the term head to measure the kinetic energy which a pump creates. Head is a measurement of the height of a liquid column which the pump could create resulting from the kinetic energy the pump gives to the liquid (imagine a pipe shooting a jet of water straight up into the air, the height the water goes up would be the head). The main reason for using head instead of pressure to measure a centrifugal pump's energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not change. So we can always describe a pump's performance on any Newtonian fluid, whether it's heavy (sulfuric acid) or light (gasoline) by using the term head.
 * Remember, head is related to the velocity, which the liquid gains when going through the pump.

www.pskf.ca Glossary of construction and engineering technology
 * Dynamic head: the total equivalent head drop due to the static head and all friction losses.
 * Discharge: volume of water pumped at a specific head.
 * Static head: vertical distance from inlet water elevation to discharge elevation.