A screw pump (also known as an Archimedean screw) conveys water or sludge-containing liquids based on the Archimedean principle. A spiral-shaped screw rotates within an inclined pipe or trough, gently lifting the conveyed medium upwards. This allows large volumes of liquid or liquid-solid mixtures to be continuously transported to a defined height. Thanks to its slow rotational speed, the pump operates very reliably and is well suited for irregular inflow conditions.

Screw pumps are mainly built in two designs: closed pipe screw pumps and open trough screw pumps. In the pipe screw pump, an internal core pipe with welded screw flights rotates inside an outer pipe casing. This closed design does not require a separate concrete bed and is ideal for retrofitting into existing pump shafts. In contrast, the trough screw pump operates without an outer pipe. Here, the screw is installed openly in a channel formed by a concrete or steel trough. Thanks to this open design, the water can be discharged at the upper end of the screw into the on-site outflow channel.

Screw pumps can usually be integrated into existing systems without major effort. Pipe screw pumps with a fixed outer casing are particularly well suited for retrofitting into existing inlet structures, as no additional concrete bed is required. For new installations, prefabricated compact units or steel troughs are often supplied, with the screw already installed. These are lifted into place on-site as a complete unit.

Screw pumps offer several advantages: they operate robustly and reliably, even under harsh conditions. Unlike many centrifugal pumps, screw pumps are less prone to clogging, as they can convey solids and fibrous materials with ease. The low rotational speed and volumetric conveying principle gently handle the medium (e.g. living organisms), and make the pump dry-run safe and self-regulating – meaning the flow rate automatically adjusts to fluctuating inflow conditions. Thanks to their high efficiency, low maintenance needs, and simple construction, screw pumps are particularly maintenance-friendly and cost-effective. Compared to centrifugal or progressive cavity pumps, screw pumps often result in lower operating and life cycle costs for the same conveying task.

The choice of screw pump depends on the degree of treatment of the medium. For untreated raw wastewater, an open steel or concrete trough screw pump is recommended, as it is robust and can easily handle coarse solids. For pre-treated wastewater, all designs are suitable – including the closed pipe trough screw pump, since the solid content is lower. For return sludge, all variants can also be used, though the closed pipe trough screw pump is often the most economical choice due to its compact design, better odor containment, and higher energy efficiency.