A screw pump , also known as a water screw , is a positive-displacement (PD) pump that uses one or several screws to move a fluid solid or liquid along the screw(s) axis. Is. In its simplest form ( Archimedes’ screw pump ), a single screw rotates in a cylindrical cavity, moving material along the axis of the screw. This ancient construction is still used in many low-tech applications, such as irrigation systems and in agricultural machinery to transport grain and other solids. The development of screw pumps has led to a variety of multi-axis technologies where carefully crafted screws rotate in opposite directions or remain stationary within a cavity. The cavity can be profiled, creating cavities where the pumped material is “trapped”.
In offshore and marine installations, three-axle screw pumps are often used to pump high-pressure viscous fluids . Three screws propel the pumped liquid forward into a closed chamber. As the screws spin in opposite directions, the pumped liquid moves along the screw’s spindle.
Three-spindle screw pumps are used to transport viscous liquids with lubricating properties. They are suitable for a variety of applications such as fuel-injection , oil burner , boosting, hydraulics , fuel, lubrication , circulation, feed, etc.
Compared to centrifugal pumps , positive-displacement pumps have several advantages. The pumped fluid is moving axially without turbulence which eliminates the foam that would otherwise occur in viscous fluids. They are able to pump liquids of high viscosity without losing the flow rate. Furthermore, the change in pressure difference has little effect on PD pumps compared to centrifugal pumps.
The term ‘screw pump’ is often used generically. However, this generalization can be a disadvantage as it fails to recognize the individual product or ‘screw’ configurations, as well as the uses, advantages and design considerations for each. The design differences of each screw configuration and pump type make each suitable for different applications and handling liquids with different characteristics.
Each ‘screw pump’ operates on the same basic principle as turning a screw to separate a volume of fluid and convey it. However, the mechanical design of each is different. The primary difference is the number of screws: one, two, three or more.
History
The screw pump is the oldest positive displacement pump. [1] The first record of a water screw, or screw pump, dates back to ancient Egypt before the 3rd century BCE . [1] [2] The Egyptian screw, which was used to lift water from the Nile , was made of tubes wound around a cylinder; As the entire unit rotates, the water is lifted to a higher height within the spiral tube. A later Egyptian screw pump design had a spiral groove cut out of a solid wooden cylinder and then the cylinder was covered with a metal board or sheet that closely covered the surfaces between the grooves. [1]
A cuneiform inscription from the Assyrian king Sennacherib (704–681 BC) has been interpreted by Stephanie Daly [3] to describe a casting water screw in bronze about 350 years ago. This is in line with the classical writer Strabo , who describes the hanging garden as irrigated by screws. [4]
The screw pump was later brought to Greece from Egypt. [1] It was described by Archimedes , [5] on the occasion of his visit to Egypt , around 234 BC. [6] This suggests that the instrument was unknown to the Greeks before the Hellenistic period.
