A screw pump is a

positive-displacement pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they ...

that use one or several screws to move fluid solids or liquids along the screw(s) axis. Three principal forms exist; In its simplest form (the Archimedes' screw pump or 'water screw'), a single screw rotates in a cylindrical cavity, thereby gravitationally trapping some material on top of a section of the screw as if it was a scoop, and progressively moving the material along the screw's axle until it is discharged at the top. This ancient construction is still used in many low-tech applications, such as irrigation systems and in agricultural machinery for transporting grain and other solids. The second form works differently; it squeezes a trapped pocket of material against another screw. This form is what is typically referred to in modern times with the term 'screw pump'. The third form (the progressive cavity pump or eccentric screw pump) squeezes a trapped pocket of material against the cavity walls by spinning the screw eccentrically. Like all positive-displacement pumps, all various kinds of screw pumps function by trapping a volume of material somehow, and then moving it. There are numerous ways to shape the screw or the cavity to accomplish this function, and the number of screws working together can be many. The term 'screw pump' refers generically to all of these types. However, this generalization can be a pitfall as it fails to recognize that the different ‘screw' configurations have different advantages and design considerations for each, which lead to the various kinds being suitable for very different use cases, material types, flow rates, and pressures. One of the most common configurations of a screw pump is the three-spindle screw pump. Three screws press against each other to form pockets of the pumped liquid in the grooves of the screws. As the screws rotate in opposite directions, the pumped liquid moves along the screws' spindles. There is nothing magical about two, three or any number of screws; pockets are formed regardless. Three rather than two spindles are used because this allows the central screw to experience symmetrical pressure loading from all sides. This ensures that the central screw is not pushed sideways, will not be bent, and thus eliminates the need for radial bearings on the main axle to absorb radial forces. The two side screws can then be made as internally-hidden free-floating rollers, lubricated by the pumped liquid itself, thus eliminating the need for bearings on those axles. This is commonly desired because seals and bearings on machines are common sources of failure. Three-spindle screw pumps are most often used for transport of viscous fluids with lubricating properties. They are suited for a variety of applications such as

fuel-injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All compr ...

oil burner An oil burner is a heating device which burns #1, #2 and #6 heating oils, diesel fuel or other similar fuels. In the United States ultra low #2 diesel is the common fuel used. It is dyed red to show that it is road-tax exempt. In most markets ...

s, boosting,

hydraulics Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...

, fuel,

lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...

, circulating, feed, and to pump high-pressure viscous fluids in offshore and marine installations. Compared to various other pumps, screw pumps have several advantages. The pumped fluid is moving axially without turbulence which eliminates foaming that would otherwise occur in viscous fluids. They are also able to pump fluids of higher viscosity without losing flow rate. Also, changes in the pressure difference have little impact on screw pumps compared to various other pumps. There is also very little back-drive on the power axle, and the output of the flow is typically very even and doesn't pulsate much.

History

The screw pump is the oldest positive displacement pump. The first records of a water screw, or screw pump, dates back to Ancient Egypt before the 3rd century BC. The Egyptian screw, used to lift water from the

Nile The Nile, , Bohairic , lg, Kiira , Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered the longest riv ...

, was composed of tubes wound round a cylinder; as the entire unit rotates, water is lifted within the spiral tube to the higher elevation. A later screw pump design from Egypt had a spiral groove cut on the outside of a solid wooden cylinder and then the cylinder was covered by boards or sheets of metal closely covering the surfaces between the grooves. A

cuneiform Cuneiform is a logo- syllabic script that was used to write several languages of the Ancient Middle East. The script was in active use from the early Bronze Age until the beginning of the Common Era. It is named for the characteristic wedge- ...

inscription of

Assyria Assyria ( Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the A ...

n king

Sennacherib Sennacherib ( Neo-Assyrian cuneiform: or , meaning " Sîn has replaced the brothers") was the king of the Neo-Assyrian Empire from the death of his father Sargon II in 705BC to his own death in 681BC. The second king of the Sargonid dynas ...

(704–681 BC) has been interpreted by

Stephanie Dalley Stephanie Mary Dalley FSA (''née'' Page; March 1943) is a British Assyriologist and scholar of the Ancient Near East. She has retired as a teaching Fellow from the Oriental Institute, Oxford. She is known for her publications of cuneiform ...

Stephanie Dalley, ''The Mystery of the Hanging Garden of Babylon: an elusive World Wonder traced'', (2013), OUP to describe casting water screws in bronze some 350 years earlier. This is consistent with classical author

Strabo Strabo''Strabo'' (meaning "squinty", as in strabismus) was a term employed by the Romans for anyone whose eyes were distorted or deformed. The father of Pompey was called " Pompeius Strabo". A native of Sicily so clear-sighted that he could s ...

, who describes the

Hanging Gardens The Hanging Gardens of Babylon were one of the Seven Wonders of the Ancient World listed by Hellenic culture. They were described as a remarkable feat of engineering with an ascending series of tiered gardens containing a wide variety of tre ...

as watered by screws. The screw pump was later introduced from Egypt to Greece. It was described by

Archimedes Archimedes of Syracuse (;; ) was a Greek mathematician, physicist, engineer, astronomer, and inventor from the ancient city of Syracuse in Sicily. Although few details of his life are known, he is regarded as one of the leading scientis ...

, on the occasion of his visit to

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...

, circa 234 BC. This suggests that the apparatus was unknown to the Greeks before

Hellenistic In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in ...

times.

References

{{Reflist Pumps Screws Egyptian inventions

History

See also

References