🔍 Key Concepts

• Look at where items #68 and #78 are located in relation to the impeller and casing – are they on the shaft, in the bearing housing, or at the impeller/casing clearance? • Understand the difference between wearing rings (replaceable rings to control leakage and protect expensive parts) and journal bearings (support the shaft). • Know what shaft keyways and bearing retainers or spacers physically look like and where they are usually placed on a centrifugal pump shaft.

💭 Think About

• Ask yourself: Are items #68 and #78 drawn as thin rings that form a close clearance between the rotating impeller and the stationary casing, or are they solid blocks supporting the shaft? • Do the arrows point to a cut or slot in the shaft (which would suggest a keyway) or to components around the outside of the shaft that keep the bearings in position? • If these parts wear out from small leakage flow but are easy and cheap to replace, which of the listed components are designed for that purpose?

✅ Before You Answer

• Verify whether #68 and #78 are stationary or rotating parts in the illustration. • Check if they are placed at the eye or outer edge of the impeller where leakage control is important. • Confirm that their primary function matches the description in your study materials before choosing your answer.