Single screw pump working principle, characteristics and selection method

● Working Principle of the Pump

A single-screw pump is a type of positive displacement pump that operates using an eccentric helical rotor and a flexible stator with a double-helix structure. As the rotor rotates within the stator, it creates a series of sealed chambers that move along the spiral path. This movement allows the fluid to be continuously and uniformly transported from the inlet to the outlet, making it ideal for handling various types of media under different conditions.

● Suitable Applications

Single-screw pumps are particularly well-suited for transporting high-viscosity fluids, ranging from 37,000 to 200,000 centipoise depending on the pump size. They can also handle media containing solid particles or fibers, with particle diameters up to 30 mm (not exceeding the rotor's eccentricity) and fiber lengths up to 350 mm (equivalent to 0.4 times the rotor pitch). The solids content can be as high as 40%, and if the solids are fine powders, it can go up to 60% or more. These pumps are ideal when stable pressure is required and the medium must not be damaged during transport.

● Key Features of the Pump

Compared to other pump types such as piston, centrifugal, vane, and gear pumps, single-screw pumps offer several advantages: - They can handle media with high solid content. - They provide a steady and uniform flow, especially at low speeds. - Flow rate is directly proportional to the pump speed, allowing for excellent variable control. - A single pump can transport different viscosity media. - Installation can be done in any orientation. - They are suitable for sensitive materials that may be damaged by centrifugal force. - They are compact, lightweight, quiet, simple in design, and easy to maintain.

● Industrial Applications

Single-screw pumps are widely used across various industries, including: - Chemical industry: acids, alkalis, salts, viscous pastes, and chemical slurries. - Mining and exploration: drilling muds, mining water, pulp, and slurry. - Shipbuilding: bilge water, oily water, and various oils. - Ceramics: clay, glaze, and ceramic slurries. - Energy sector: fuels, coal-oil slurry, coal-water slurry, and waste materials. - Wastewater treatment: sewage, sludge, and slurry. - Paper industry: cellulose pulp, paints, and black liquor. - Food and pharmaceuticals: grain pulps, starch pastes, syrups, and wine residues. - Agriculture, forestry, and aquaculture: wide-ranging applications exist in these fields as well.

● Pump Selection Guidelines

When selecting a single-screw pump, the key factors include the properties of the fluid being transported, the required pressure, and the viscosity of the liquid. For non-corrosive liquids like water, the pump can operate at its maximum design speed. However, in real-world applications, it’s generally recommended to run the pump below this speed, especially when handling high-viscosity or particulate-laden media. Typically, the speed should be reduced to 1/2 to 1/3 of the design speed. Operating at lower speeds helps reduce wear, but as the stator wears over time, the speed can be increased slightly to compensate for reduced flow. The operating temperature should be between -10°C and 80°C, with special cases up to 120°C. The maximum pressure per stage is 0.6 MPa, with short-term capacity up to 0.8 MPa (for less than 30 minutes). As the pump wears, the volumetric efficiency will gradually decrease at the same output pressure. The maximum suction height for water is 8 meters, but it is recommended not to exceed 6.5 meters in practice. For high-viscosity media, positive pressure suction is advised.

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