Centrifugal pump design and construction 33
The shaft design depends on the evaluations of either the torsion shear stress at the
smallest diameter of the shaft or a comprehensive fatigue evaluation taking into
consideration the combined loads, the number of cycles, and the stress concentration
factors. The design at all times involves sophisticated finite-element computer evaluations.
The shaft design is limited not only to the stress evaluation but is also dependent on
other factors such as:
• Shaft deflection
• Key stresses
• Mounted components
• Critical speeds (rotordynamics).
The most common pump shaft material is plain carbon steel, typically BS-970-En 8.
Higher grades include BS-970-En19 or AISI 4140, ASTM-A322, Grade-4140
(quenched ...