Renewable Energy Design

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