Hydrogen cooled well below zero poses particular challenges to the components used, especially the moving ones. The ball bearings of submersible pumps for pumping cryogenic media are examples of such heavily burdened parts. That is why NSK, a company originated in Tokyo, has developed self-lubricating deep groove ball bearings that work without the need to apply a separate lubricant.
Friction-reducing agents other than the pumped media are not used, which is normally tribologically unfavorable. Pumps designed for cryogenic applications have a double-row bearing arrangement of the pump shaft, where the inner and outer rings are made of special corrosion-resistant steel. The stainless steel NSK bearings have a wear-resistant cage made of self-lubricating fluoroplastic so that cryogenic gases such as GH2 (gaseous hydrogen) or LNG (liquefied natural gas) can be pumped at down to -200 °C.
The European rolling bearing manufacturer NSK Europe Ltd. now offers a whole range of deep groove ball bearings specially designed for these unusual operating conditions – with shaft diameters from 30 to 100 mm. They tolerate very low temperatures as well as rotational speeds of up to 3,600 min-1 and are suitable for hydrogen refueling stations as well as for larger pumping stations.
