I looked after about 1500 pumps in a nuke plant and I agree with Perry. Angular contact bearing pairs must be shimmed or matched so that the axially unloaded bearing (not the loaded) is still preloaded enough to ensure the balls roll and don't skid. Skidding causes nasty damage to happen. Modern Vortec blowers which spin up to thousands of rpm are supported by tiny angular contact bearing pairs and your best bet for a good rebuild is to send them back to Vortec, IMO. It's that tricky to set them up.
And I agree with David. The holes in the impeller back shroud are to reduce axial load on the shaft bearings. This is common practice in pump design. The holes bleed the discharge pressure seen on the back side of the impeller back to the suction side. This reduces the thrust load towards the suction side.
Malcolm
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