Enclosed, open, and semi-closed are terms used for designation and selection of impellers.

• A. Lantern Rings
• B. Sleeves
• C. Stuffing Boxes
• D. Impellers

Answer: (D)

These terms describe the design of impellers in centrifugal pumps. The way blades are arranged and protected by surrounding walls determines how the pump handles flow and solids, as well as its efficiency.

Enclosed (or closed) impellers have blades sandwiched between two shrouds. This design creates a smooth, high-efficiency flow and is best for clean liquids or those with little solids, providing higher head and better suction performance.

Open impellers have blades connected directly to the hub with no front or back shroud. They’re more robust for handling solids and fibrous materials and are easier to maintain, but they generally offer lower efficiency and require stricter pipe and casing clearances.

Semi-closed (or semi-open) impellers have one shroud, offering a compromise between the two: improved efficiency over open designs while still providing better solids handling than fully enclosed ones.

The other terms listed—lantern rings, sleeves, stuffing boxes—are components related to packing seals around a shaft, not to the design of the impeller itself.

So the terms enclosed, open, and semi-closed correctly pertain to designation and selection of impellers.