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

• A. Impellers
• B. Pumps
• C. Valves
• D. Gaskets

Answer: (A)

These terms describe the design of the pump impeller—the rotating part that pushes fluid. An impeller can be open (no outer cover on the blade sides), semi-open (one side shielded by a shroud), or enclosed/closed (shrouds on both sides). The choice affects how well the pump handles solids and how efficiently it moves fluid. Open impellers are often better for fluids with solids because debris can pass through more easily, while closed impellers offer higher efficiency for cleaner liquids but are more prone to clogging with solids. Semi-open impellers provide a middle ground. Since the designation of enclosed, open, and semi-closed specifically refers to the impeller’s construction, they’re used for selecting impellers, not for other components like pumps as a whole, valves, or gaskets.