Screw pumps are primarily classified according to the number of their working screws. Common types include single-screw pumps, twin-screw pumps, and three-screw pumps, as well as multi-screw pumps (such as five-screw pumps).
A single-screw pump is an internally meshing eccentric rotary positive displacement pump, mainly consisting of a single-headed helical rotor (eccentric screw) and a stator (bulb) typically made of elastic material with a double-ended helix. Single-screw pumps can transport media with high solids content, providing uniform flow and stable pressure. They can transport high-viscosity media, and even media containing gases and solid particles or fibers.
A twin-screw pump is an externally meshing screw pump, utilizing two meshing, non-contacting screws to pump liquids. Twin-screw pumps are non-hermetic positive displacement pumps, capable of transporting not only pure liquids but also mixtures of gases and liquids (gas-liquid mixing). They possess strong self-priming capabilities and allow for short periods of dry running. Twin-screw pumps have a wide flow range (1–1800 m³/h) and are suitable for conveying various lubricating or non-lubricating media with a wide viscosity range (1–200,000 mm²/s).
Three-screw pumps typically consist of one driving screw, two meshing driven screws, and a bushing enclosing the three screws, forming a sealed cavity. Three-screw pumps offer good sealing performance and high volumetric efficiency, and are commonly used to convey clean media with a certain degree of lubrication, such as lubricating oil, fuel oil, and medium-viscosity oils. They are widely used in industries such as machinery, petroleum, chemical, metallurgy, steel, power, shipbuilding, and building materials.
Besides being classified by the number of screws, screw pumps can also be classified by suction method (single-suction and double-suction) and by pump shaft position (horizontal and vertical).
