Screw pump
Oldest positive-displacement pump, using screws to move materials.
A screw pump is a type of positive-displacement pump that moves fluids or solid materials along the axis of one or more rotating screws. It holds the distinction of being the oldest known positive-displacement pump, with evidence of its use in Ancient Egypt before the 3rd century BC.
The earliest Egyptian design consisted of tubes wound around a cylinder; as the whole assembly turned, water was lifted up the spiral tube. A later version featured a spiral groove carved into a solid wooden cylinder, which was then covered with boards or metal sheets. An Assyrian cuneiform inscription from the reign of King Sennacherib (704–681 BC) has been interpreted as describing bronze water screws cast some 350 years earlier, consistent with the classical writer Strabo’s account of the Hanging Gardens being watered by screws. The device later reached Greece, where Archimedes described it around 234 BC after visiting Egypt, suggesting it was unknown to the Greeks before the Hellenistic period.
Three main designs exist. The simplest, the Archimedes’ screw, uses a single screw rotating in a cylindrical cavity. Material is trapped on top of the screw’s sections like a scoop and moved upward along the axle until discharged. This ancient form is still used in low-tech applications such as irrigation and moving grain. The second design works by squeezing a trapped pocket of material against another screw; this is the type most commonly referred to as a screw pump today. The third, the progressive cavity or eccentric screw pump, squeezes material against the cavity walls by spinning the screw off-center.
Like all positive-displacement pumps, screw pumps work by trapping a volume of material and then moving it. The screw and cavity can be shaped in many ways, and multiple screws can work together. The term “screw pump” covers all these types, but this broad label can be misleading because different screw configurations offer distinct advantages and design considerations, making them suitable for very different uses, materials, flow rates, and pressures.
A common configuration is the three-spindle screw pump. Three screws press against each other to form pockets of liquid in their grooves. As the screws rotate in opposite directions, the liquid moves along the spindles. Pockets form regardless of the number of screws, but three spindles are used because the central screw experie
- type
- Positive-displacement pump
- earliest_record
- Ancient Egypt, before 3rd century BC
- known_for
- Lifting water and moving fluids/solids via rotating screws
- principal_forms
- Three: Archimedes' screw, modern screw pump, progressive cavity pump
- common_configuration
- Three-spindle screw pump
Lore & Background
The first records of a water screw, or screw pump, date back to Ancient Egypt before the 3rd century BC. The Egyptian screw, used to lift water from the Nile, was composed of tubes wound round a cylinder; as the entire unit rotates, water is lifted within the spiral tube to a higher elevation. A later design from Egypt had a spiral groove cut on the outside of a solid wooden cylinder, then covered by boards or sheets of metal. A cuneiform inscription of Assyrian king Sennacherib (704–681 BC) has been interpreted by Stephanie Dalley to describe casting water screws in bronze some 350 years earlier, consistent with classical author Strabo describing the Hanging Gardens as watered by screws. The screw pump was later introduced from Egypt to Greece and described by Archimedes circa 234 BC, suggesting the apparatus was unknown to the Greeks before Hellenistic times.
Reader's Guide
The screw pump is significant as the oldest positive-displacement pump, with a history spanning over two millennia. Its three principal forms—the Archimedes' screw, the modern screw pump, and the progressive cavity pump—each trap and move material differently, suiting various applications from low-tech irrigation to high-pressure industrial uses. The three-spindle configuration, where three screws press against each other, allows the central screw to experience symmetrical pressure loading, eliminating the need for radial bearings and reducing failure points. Screw pumps offer advantages such as axial fluid movement without turbulence (preventing foaming), ability to pump high-viscosity fluids without losing flow rate, minimal impact from pressure changes, low back-drive on the power axle, and even, non-pulsating output. They are commonly used for viscous fluids with lubricating properties in fuel-injection, oil burners, hydraulics, and offshore installations. The term 'screw pump' generically refers to all types, but different configurations have distinct design considerations and use cases.
Did You Know?
- The screw pump is the oldest positive displacement pump, with records from Ancient Egypt before the 3rd century BC.
- A cuneiform inscription of Assyrian king Sennacherib (704–681 BC) has been interpreted to describe casting water screws in bronze.
- The screw pump was described by Archimedes circa 234 BC after his visit to Egypt.
- Three-spindle screw pumps eliminate the need for radial bearings on the main axle by symmetrical pressure loading.
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