Screw pumps are mainly classified according to the number of their working screws. Common types include single-screw pumps, twin-screw pumps, and three-screw pumps. In addition, there are multi-screw pumps (such as five-screw pumps).
A single-screw pump is an internally meshing eccentric rotary positive displacement pump, mainly composed of a single-headed helical rotor (eccentric screw) and a stator (bulb) with double-ended helices, usually made of elastic material. Single-screw pumps can transport media with high solid content, with uniform flow and stable pressure. They can transport high-viscosity media, and even media containing gas and solid particles or fibers.
Twin-screw pumps are externally meshing screw pumps that use two meshing, non-contacting screws to pump liquids. Twin-screw pumps are non-sealed positive displacement pumps. In addition to transporting pure liquids, they can also transport mixtures of gas and liquid, i.e., gas-liquid mixed transport. They have strong self-priming capabilities and allow short-term dry running [8]. 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).
