Question : How long do the bearings last in a turbopump?
Answer :
Most turbopumps are fitted with ceramic coated ball bearings which are lubricated with grease or oil. After some time in operation the bearings become worn leading to excessive noise, vibration and ultimately seizure.
Several factors can influence the lifetime of the bearings, the most important one is their operating temperature. Users must ensure that the turbopump is adequately cooled, either using water cooling or forced air cooling if the ambient air is cool enough. The pump's duty cycle can also influence life, as frequent stop/start operation, or pumping high gas loads for prolonged periods of time can increase the heat of the pump rotor due to gas compression and this heat must be dissipated by conduction through the bearings to the cooled pump body.
In general, bearing lubrication by oil is believed to be preferable to grease lubrication as the grease has a tendency to dry out over time and reduce its lubricating ability, especially if high operating temperatures are encountered. Edwards EXT turbopumps use oil lubrication, the oil circuit is sealed for life and incorporates a filter to continuously remove any particulates generated through oxidation and hence retain the best lubrication capability over a long time. They also incorporate a passive magnetic upper bearing which is completely clean and requires no maintenance, this halves the number of bearings in the pump and allows the design to be optimised around the single lower bearing, as well as reducing noise and vibration levels.
If long service life is important, users could also consider Edwards STP series magnetic levitation turbopumps where the rotor is suspended in a magnetic field with no bearing contact and therefore no maintenance required. These pumps are available in sizes from 300 l/s to 4500 l/s. For more information, visit Edwards Turbo Pumps minisite or call AVT on 1800 55 99 88.
