BB Type Centrifugal Pumps

Some Multistage pumps only have 2 bearings, and as it is a BB (between bearing) pump, the bearings are always going to be outboard.

For multi-bearing pumps, I suspect that it has to do with the limited strength of the housing between stages to withstand the thrust, and as only one thrust bearing is required, placing it at one end would appear to be logical.

Fewer differential expansion problems, plus it's a lot easier to align/check/replace when it's on the NDE (Non Drive End).

Lets say you would put them mainly on the inner side: What could be the problem and is it more problematic than placing them out boards?

F_fs + F_bs + Finlet + Fmom + Fbus = Tax

Equation 1 is referred to a control volume containing all the rotating walls; Ffs is the global force acting on the front shroud walls while Fbs is relative to the back shroud, Finlet is due to the pressure field at the impeller inlet section, Fmom is the momentum contribution in axial direction and

Fbus is the pressure integral on the bushing walls.all these contribute axial thrust.now,which direction these thrust load act ? there are two direction one towards pump non drive end another one towards pump drive end / motor or prime mover.from the above equation the axial thrust load acting towards pump drive end is totally taken care by the balancing drum /disc / equalising line what ever! F_fs + F_bs+ Finlet axial thrust load acting towards pump non drive end needs an thrust bearing.

Because the thrust bearings have to have a shoulder on the shaft to seat against to take up the loading. The shoulders on the shaft have to be outboard of the impeller(s) and the seals or how else does one slide/press those items onto the shaft and since the bearings do not want to be in the fluid they are located even further outboard of the seals at the smaller diameters of the shaft.