What does a rotary pump primarily do to move liquids?

A rotary pump primarily functions by rotating screws or lobes, which is fundamental to its design and operation. This mechanism allows the pump to move liquids by trapping them in the spaces between the rotating elements and the pump casing. As these elements turn, they create a continuous flow of liquid, effectively pushing it through the discharge outlet.

In contrast, other methods such as utilizing pistons, creating a vacuum, or relying on gravity do not apply to the rotary pump's operation. Piston pumps use reciprocating motion rather than a rotary action, and while some pumps use a vacuum to draw liquids in, a rotary pump does not rely on vacuum creation for its primary function. Gravity, on the other hand, is a passive force and does not actively move liquids in the same way a rotary pump does. Therefore, the rotation of screws or lobes is the defining characteristic that enables a rotary pump to efficiently and effectively transfer liquids.