Stuffing boxes are primarily used to keep ___________ out of pump shafts

Stuffing boxes are mechanical devices used in pumps and other rotating equipment to create a seal around the shaft. Their primary function is to prevent air and other contaminants from entering the pump casing through the shaft's opening. This is crucial for maintaining the efficiency of the pump and ensuring that the fluid being pumped does not leak out, which could lead to system failure or environmental hazards.

By keeping air out of the pump shafts, stuffing boxes help maintain the proper pressure and vacuum conditions needed for effective operation. If air were to enter the system, it could cause various issues, including reduced efficiency, cavitation, and potential damage to the pump components.

In this context, the other options do not align with the primary purpose of stuffing boxes. For example, oil and horsepower are not the critical substances or forces that stuffing boxes are designed to keep out, and electricity refers to electrical systems rather than the fluid dynamics involved in pumping operations.