Archimedean screw pump

The Archimedean screw pump is used for constant-pressure lifting of a fluid to a given geodetic height with the aid of a rotating screw (true helicoid), which works on the principle of the irrigation device invented by Archimedes. See Fig. 1 Archimedean screw pump

The screw is open on all sides, can be several metres long, is usually made of sheet metal and can have up to three flights or starts. It rotates in an open, semi-circular trough inclined at an angle of approximately 30°. At each turn, the screw scoops up a limited volume of water (determined by the angle of inclination, diameter and lead or pitch of the screw) from the lower water reservoir and lifts it to the top end of the trough at a relatively low rotational speed (below 100 rpm).

Depending on the immersion depth of the screw's bottom end, the volume flow rate of the Archimedean screw pump adjusts automatically within certain limits as the volume of liquid in the individual flights changes. This operating principle presupposes that the screw is constantly submerged in the liquid to at least half the diameter of its leading screw passage and that the clearance gap width between the screw and the sheet steel or concrete trough is not too large (so as to minimise leakage).

The lower bearing is submerged (see Plain bearing) and must be lubricated with fresh water or grease. The upper bearing often is a rolling element bearing and also absorbs axial forces The gear unit is coupled to the upper end of the screw.

Archimedean screw pumps are capable of pumping heavily contaminated surface water or sewage, and even sand if they are specially designed for this purpose. The head is purely geodetic and ranges up to 6 m at efficiencies between 60 and 80 %. Depending on the flow rate the screw diameter can be up to several metres. Archimedean screw pumps are simple, adapt easily to operating conditions and operate economically. However, they frequently have to compete with submersible motor pumps.