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Alfa Laval three-screw pump

The thoroughly engineered 3S series is suitable 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 ensuring a high degree of flexibility when specifying a pump for specific system designs.


The 3S series consists of a broad range of pump sizes for lubricating, non-abrasive oil based liquids.
3S pumps are used in marine and industrial applications.

Examples are:

  • Feed and circulation pumps for fuels and lubricants
  • Lubricant and coolant pumps for gears, engines and hydraulic systems
  • Feed and transfer pumps for oil burner technology


Key benefits significant to the 3S pump design are:

  • Minimized life cycle cost
  • Low maintenance
  • High quality
  • Environmentally friendly
  • High volumetric efficiency
  • High energy efficiency


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. Consequently, the 3S series ischaracterised by an innovative design for long service life, even in harsh operating conditions.

Technical data


Pump casing Nodular cast iron, EN-GJS-400
Screws Nitration-hardened steel, 1.7139
Seal faces, mechanical seal SiC/hard metal

Port connections

Flanges PN16 according to EN 1092-1 type B1/B2, in inline configuration or at the top. For 3S BT and 3S VT special counter flanges are required. A special flange design is used with 3S BS pumps.


According to the IEC metric standard:

  • 2 poles = 2,900/3,500 rpm at 50/60 Hz
  • 4 poles = 1,450/1,750 rpm at 50/60 Hz
  • 6 poles = 950/1,200 rpm at 50/60 Hz
  • IP55, insulation class ICLF, efficiency class IE2

Design features