The 3S three-screw pumps consist of a broad range of low maintenance pumps for lubricating, non-abrasive and chemically inert liquids. 3S pumps are the best choise in many various industrial applications.

fluid handling

A universal design

The 3S series has been thoroughly engineered and is applicable for various applications. With a range consisting of 29 different pump sizes with delivery rates from 5 – 2.900 l/min @ 1450 rpm the 3S series is one of the most comprehensive three-screw pump ranges available on the market. 

Furthermore, the individual pump sizes are available in several executions, which ensures a high degree of flexibility when specifying a pump for specific system designs.

Low maintenance

The 3S series pump is designed with a lifetime-lubricated external ball bearing with an expected  lifetime of 30.000 hours. With a weep hole just between the shaft seal and the bearing, preventing accumulation of residue the bearing is well protected. The ball bearing is not exposed to the pumped liquid. The mechanical seal is well lubricated and cooled. The seal is designed to efficiently dissipate frictional heat.

Magnetic coupled version

The 3S pumps are also available in a magnetic coupled version. The pump is hermetically sealed and the liquid cannot escape or react by coming into contact with other materials.

Como funciona

The basic principle of the 3S screw pump is that the turning screws isolate fluid and convey it. The conveyance thus takes place through the axial displacement of closed volumes.

The rise in pressure is directly related to the length of the screws.




Operating principle

Three-screw pumps are rotary positive displacement pumps. By the meshing of the three rotating screws and the enclosing pump casing the displacement effect is created. The screws are radially supported by the sliding contact in the casing, which requires lubrication by the pumped liquid. The axial support of the main screw is carried out by a ball bearing.

The pump is equipped with an internal relief valve which will limit the differential pressure and protect the pump from excessive pressure. On the Alfa Laval 3S pump the valve setting is adjustable to different opening pressures .


3S casings are of nodular graphite iron, EN-GJS-400, and screws are of nitrated steel 1.7139. High quality mechanical seal with special SiC graphite material as standard.

3S pumps are available in several executions, e.g. with free shaft end, as a unit on bracket foot or vertical pedestal. Furthermore, each pump size is available in inline as well as top flange design.

Advantages of the 3S three-screw pump design:

  • Low lifecycle cost
  • Long life time and low maintenance
  • Compact design
  • High capacity at limited space
  • High efficiency
  • Low noise
  • Low pulsation
  • Pumping without violent turbulence
  • Very good suction conditions (NPSH)