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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.
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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.
219:), 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
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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
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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
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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
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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
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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.
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or eccentric screw pump) squeezes a trapped pocket of material against the cavity walls by spinning the screw eccentrically.
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The screw pump is the oldest positive displacement pump. The first records of a water screw, or screw pump, dates back to
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to describe casting water screws in bronze some 350 years earlier. This is consistent with classical author
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with lubricating properties. They are suited for a variety of applications such as
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The screw pump was later introduced from Egypt to Greece. It was described by
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The
Mystery of the Hanging Garden of Babylon: an elusive World Wonder traced
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before the 3rd century BC. The
Egyptian screw, used to lift water from the
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Principle of screw pump (Saugseite = intake, Druckseite = outflow)
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Three-spindle screw pumps are most often used for transport of
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Three principal forms exist; In its simplest form (the
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One hundred greatest science inventions of all time
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334:. The Encyclopaedia Britannica Co. 2011
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