This paper addresses a common gap in pump transmission design that relies on “allowable stress + safety factor.” This paper redesign a complete shaft key coupling bearing train of a 5.5 kW/1450 rpm centrifugal pump using a reliability based framework. A field case uses nameplate data and dimensional measurements. Methods include ASME/DE von Mises formulation for combined bending torsion, stress concentration factors for keyseat/fillet, consistent torque path sizing of key and flange coupling, and bearing L10 life per ISO 281. All calculations use SI units with ±5–10% uncertainty propagation. Results show an S40C shaft ds≈33.3 mm, a 10×8×15 mm key, a flange coupling passing shear/crushing checks, and an angular contact bearing meeting a 20–40 kh life target, sensitivity highlights Kt and equivalent bearing load as dominant drivers. This paper recommend as a design for reliability guide for maintenance friendly pump trains in SME/utility settings, complemented by targeted vibration tests.
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