New Equipment

Externally pressurized porous (EPP) gas bearings enable significant machine innovation. They combine the advantages of many bearing types; the load capacity of oil bearings. Zero friction and adjustability of magnetic bearings, yet can be hot immersed in the process like a foil bearing.

Review some of the features that could differentiate your next design in the list below:

  • Eliminate oil and barrier seals
  • Operation to 400C on process gas (hot immersed)
  • Unit loading to 400 psi
  • Eliminate shear losses
  • Operate at higher speed
  • Effectively zero cross coupled stiffness
  • EPP gas bearing may operate directly on an impeller
  • EPP gas bearings provide gas sealing too
  • Fit in the same space as oil bearings
  • Reduce impeller tip clearances
  • Reduce space and costs of services
  • Eliminate oil system
  • Simplify seal panel

Performance Characteristics of Bearing Types

Oil Journal Active Magnetic Bump Foil Flex/Pivot Hybrid Oil Pressurized Gas
Friction at Start 1 3 1 2 3
Heat Generation 1 3 2 1 3
Process Compatibility 1 2 3 1 3
Shear/Loss and Speed 1 3 2 1 3
Load Capacity 3 2 1 3 3
Damping 2 3 1 3 2
Cost 3 1 3 2 2
Service Cost 1 2 3 1 2
Total 13 19 16 14 21
Rating Key: 3=Best 2=Average 1=Worst
The chart above compares some common bearing types with their characteristics. Pressurized gas bearings have some powerful attributes and although accepted in other industries, they have little acceptance in the rotating equipment industries.
Additionally, externally pressurized bearings offer new options in machine architecture. For instance, hydro and aerodynamic thrust bearings have segmented pads for the purpose of having leading edges for the fluid film wedge to develop. Because of these big radial gaps no engineer would consider a dynamic thrust bearing as a seal. Thinking alternatively, externally pressurized thrust bearings have a contiguous 360-degree face that looks just like a dry gas seal face and because the pressure is always highest in the bearing gap, it is already a seal! This gets the engineer thinking “If I could eliminate oil lubrication, combine my thrust bearing with my dry gas seal, I could even use area on the thrust runner to replace the balance piston.” This dramatically reduces moving parts and brings DGS low leakages to balance pistons (the low hanging fruit of improved compressor efficiency). The biggest advantage though, as Don Bently would argue is that the shaft, which is the weak link, stiffens on a cube function as you make it shorter, dramatically improving the rotor dynamics. Reliability improves, as seal faces no longer need to follow the shaft, and there is no start and stop ware, making reliability deterministic.
Externally Pressurized Thrust Bearing
An externally pressurized thrust bearing looks and acts much like a double opposed face seal, when positioned on the high pressure side of a straight though centrifugal compressor, radial real estate on the thrust disc can be used as the balance piston, shortening the required length of shaft enough to make a big improvement in rotor dynamics.
This compressor example is just the beginning; there could be many other dramatic changes. For instance, in gas turbines, gas bearings that do not require oil or cooling and that can operate at high temperatures would be an advantage reducing services, complexity and fire hazard or large steam turbines rotors supported on steam fed bearings or power cores for sCO2 power generation with thrust bearings having 1000 psi unit loading.

So if you are interested in learning more or joining our revolution in rotating equipment, we would be glad to help.

Centrifugal Revolution

Recent and developing technological advancements could lead to some interesting future possibilities. See what Drew has to say about future compressor design.