Pumping up the action with NSK ball bearings

For use in submersible pumps that handle cryogenic gases, such as hydrogen and LNG, NSK has developed rolling bearings that do not require external lubrication. These stainless-steel bearings with a cage made of self-lubricating fluoroplastic are seeing increasing adoption in submersible pumps from leading manufacturers.

A growing number of projects worldwide are today promoting the use of hydrogen as an energy source. These projects often use special submersible pumps that can reliably pump gaseous and liquid media in continuous or intermittent operation - at low temperatures down to around -200°C.

Critical design element

In such pumps, the double bearing of the pump shaft is a critical design element. Corrosion resistance is essential, and no lubricant can be used other than the media washing around the bearing. However, this tribology is unfavourable, as it places tough demands on the material pairing. In addition, the bearings must maintain long service life, even at low temperatures.

NSK has therefore developed a series of deep groove ball bearings specifically for these exceptional operating conditions, where a number of key design features provide differentiation from conventional pump bearings. For example, the inner and outer rings are made of a stainless steel adapted to the special requirements of rolling bearings.

A stable cage that occupies the entire inner volume of the bearing provides guidance for the rolling elements (also made of stainless steel), while the cage material, a self-lubricating fluoroplastic, ensures low-friction running of the bearing, without external lubrication. In addition, the high-performance fluoroplastic is described as extremely wear-resistant and offers good low-temperature properties at speeds up to 3,600 rpm.

Longer service life

The cage is of two-piece design, with the two halves joined by stainless steel rivets. “In laboratory tests, and in practice, these deep groove ball bearings achieve significantly longer service life than other bearings for this application, such as those with a cage made from hard phenolic resin,” states NSK.

The bearings are available in various sizes (shaft diameter 30 to 100 mm) and are said to be ideal for use in both larger hydrogen pumping facilities and decentralised applications, such as hydrogen filling stations.

The bearings are also suitable for pumps handling other cryogenic gases, such as nitrogen.