A schematic of a windpump

A windpump is a windmill used for pumping water, either as a source of fresh water from wells, or for draining low-lying areas of land. Once a common fixture on farms in semi-arid areas, windpumps are still used today where electric power is not available or too expensive.

[edit] History

Windmills were extensively used in Europe, particularly in The Netherlands and the East Anglia area of Great Britain, from the middle ages onwards, to drain land for agricultural or building purposes. Early immigrants to the New World brought with them the technology of windmills which had developed in Europe.^[1]

On US farms, particularly in the Midwest, windpumps were used to pump water from farm wells for cattle. The self-regulating farm wind pump was invented by Daniel Halladay in 1854^[1][2][3]. Eventually steel blades and steel towers replaced wooden construction, and at their peak in 1930, an estimated 600,000 units were in use, with capacity equivalent to 150 megawatts.^[4] Early wind pumps directly operated the pump shaft from a crank attached to the rotor of the windmill; the installation of back gearing between wind rotor and pump crank allowed the pump to function at lower wind speeds.

[edit] Worldwide use

Brograve Mill, UK. An example of the derelict state of many Broadland Windpumps

Windpumps are used extensively in Southern Africa and Australia and on farms and ranches in the central plains of the United States. In South Africa and Namibia thousands of windpumps are still operating. These are mostly used to provide water for human use as well as drinking water for large sheep stocks.

Kenya has also benefited from the African development of windpump technologies. At the end of the 1970s, the UK NGO Intermediate Technology Development Group provided engineering support to the Kenyan company Bobs Harries Engineering Ltd for the development of the Kijito windpumps. Bobs Harries Engineering Ltd is still manufacturing the Kijito windpumps, and more than 300 Kijito windpumps are operating in the whole of East Africa.

The Netherlands is well known for its windmills. Most of these iconic structures situated along the edge of polders are actually windpumps, designed to drain the land. These are particularly important as much of the country lies below sea level.

Eight to ten-bladed windmills were used in the Region of Murcia, Spain to raise water for irrigation purposes.^[5] The drive from the windmill's rotor was led down through the tower and back out through the wall to turn a large wheel known as a noria. The noria supported a bucket chain which dangled down into the well. The buckets were traditionally made of wood or clay. These windmills were still in use until the 1950s, and many of the towers are still standing.

In the UK, the term windpump is seldom used and they are better known as Drainage windmills. Many of these were built in The Broads and The Fens, of East Anglia for the draining of land, but most of them have since been replaced by diesel or electric powered pumps. Many of the original windmills still stand in a derelict state (pictured), although some have been restored.

[edit] Construction

To construct a windpump, the bladed rotor needs to be matched to the pump. With non-electric windpumps, high solidity rotors are best used in conjunction with positive displacement (piston) pumps, because, single-acting piston pumps need about three times as much torque to start them as to keep them going. Low solidity rotors, on the other hand, are best used with centrifugal pumps, waterladder pumps and chain and washer pumps, where the torque needed by the pump for starting is less than that needed for running at design speed. Low solidity rotors are best used if they are intended to drive a electricity generator; which in turn can drive the pump. ^[6]

[edit] Windpump types

[edit] Cambered plate bladed rotor windpumps

A CP rotor bladed windpump on a farm in Iowa

"American" or more accurately, cambered plate bladed rotor windpumps can be found worldwide and are still manufactured in the United States, Argentina, New Zealand, and South Africa. A six-foot diameter windpump rotor can lift up to 180 gallons per hour of water with a 15 to 20 mile per hour wind, according to a modern manufacturer (about 700 litres/hour by a 1.8 metre rotor in 24–32 km/hour wind). Wind pumps require little maintenance, only requiring gear oil changes about once per year.^[7] Although electric pumps are now the dominant means of lifting water, an estimated 60,000 wind pumps are still in use in the United States. They are particularly economical in remote sites distant from electric power distribution.

[edit] General efficiency

Although the efficiency of a windpump is dependant on the type of bladed rotor and pump used, some general figures regarding its efficiency can be given. In general, a windpump is around 7-27% efficient. A table of the amount of water that can be displaced when there is wind is given below. ^[8][9]

[edit] Combinations

[edit] Tjasker

The "tjasker"

In the Netherlands, the "tjasker" is a popular drainage wind pump with with common sails connected to the archimedean screw. This was used for raising water in areas where only a small lift of water was required. The windshaft sat on a tripod which allowed it to pivot. The archimedean screw raised water into a collecting ring, where it was drawn off into a ditch at a higher level, thus draining the land. ^[10]

[edit] Thai windpumps

In Thailand, thai windpumps were made on Chinese windpump designs. They were constructed from wire-braced bamboo poles carrying fabric sails; a paddle pump or waterladder pump is fixed to a Thai bladed rotor. The water lift was typically less than l meter. 

[edit] See also

• Wind energy conversion system
• Comparison of bladed rotors for WECS
• Coil pump, another frequently used pump^[11]
• Loeriesfontein, Northern Cape, where there is a museum dedicated to water pumping windmills

[edit] References

[edit] External links

• Media related to Wind pumps at Wikimedia Commons
• A detailed photographic record of the restoration of an 8' Stewarts & Lloyds windpump in South Africa