The common method to secure an impeller to the shaft on a double-suction pump is what?

• A. Key
• B. Nut
• C. Pin
• D. Weld

Answer: (A)

Torque must be transmitted securely from the shaft to the impeller while keeping the impeller precisely aligned. A keyed connection provides a positive drive and exact axial positioning: a small metal key sits in matching slots (keyways) on the shaft and in the impeller bore, so rotation of the shaft directly drives the impeller without slip, and the impeller remains centered along the shaft. This arrangement is also serviceable—you can remove and replace components without damaging the shaft or impeller.

Using a nut can hold the impeller on axially, but it doesn’t reliably prevent torque slip under dynamic loads, and vibration can loosen it. A pin is less common for this purpose in high-torque pumps and complicates assembly and removal. Welding would make a permanent, non-reversible joint and could introduce stresses or damage, making future maintenance difficult. So, the keyed connection is the standard, best-fit solution.