I am sure it is a shot at me alright. However, they use a lot of "may’s and if’s" to cover there rear. Actually a Kingsbury type thrust bearing is a frictionless bearing. There is a film of water that separates the Stainless disk from the Teflon or carbon impregnated pads. As long as the bearing stays cool, it can easily handle the weight of the shaft, water, and the K factor of the impellers. The motor has to be spinning at least 1800 RPM, to cause the hydroplane effect that forms the film of water between the pads and the disk. Water is non-compress-able, so the thin film of water can hold up tremendous weights. Only if the weight is enough to physically break off a pad will the bearing fail. This is not something that happens over time. If there is too much weight for the bearing to handle, it won’t last 5 minutes. If the bearing can handle the weight, there is absolutely no friction on this type bearing, so it should last many years. Again, it is not something that is going to cause a gradual wear.
Actually it is running below 1800 RPM that destroys Kingsbury type thrust bearings. When the motor starts, there is no film of water on the bearing until 1800 RPM is achieved. Even with the quick start of an across the line starter, there is a portion of a second that the bearing runs dry. When the bearing runs without the film of water, it burns off a layer of the carbon or Teflon. Because this bearing is also what determines the spacing of the pump impellers, it is very height critical. Just a thin layer of material burned off, and not only is the bearing damaged but, the impellers can also drag. The best way to make a Kingsbury thrust bearing last, is to start the motor as fast as possible, and to have as few a starts as possible.
A soft starter or VFD is the hardest thing on Kingsbury thrust bearings. The longer it takes to get to 1800 RPM, the more wear there will be on the bearing. These variable speed units with the very small tanks, must start for every glass of water, or even when the ice maker fills. The more starts, and the slower the starts, the sooner the thrust bearing will fail.
