ADEQ Water Distribution Grade 1 Certification Practice Exam

The main idea is delivering reliable torque transmission from the shaft to the impeller while keeping them properly aligned. A key provides a positive mechanical connection: it sits in matching slots (keyways) on both the shaft and the impeller bore, so when the shaft turns, the impeller turns with it without slipping. This also helps maintain the correct axial positioning of the impeller on the shaft.

Adhesive wouldn’t hold up under the pump’s loads and vibration, and could fail or degrade over time. A pin would require precise alignment and can shear or loosen under operation. A set screw relies on friction and can loosen, slip, or mar the shaft surface, offering less reliable torque transmission. The key-and-keyway method is the standard, dependable way to couple an impeller to the shaft in a double-suction pump.