What basic operation is described by an old-fashioned hand pump?

• A. It uses a rotary mechanism to pump fluids.
• B. It is based on positive displacement operation.
• C. It generates pressure by suction.
• D. It utilizes gravity to feed liquids.

Answer: (B)

An old-fashioned hand pump operates based on positive displacement. This means that the pump moves a fixed volume of fluid with each stroke. When the handle of the pump is pulled up, it creates a vacuum that allows fluid to be drawn into the cylinder from the supply source below. When the handle is pushed down, that same fixed volume of fluid is forced out through the discharge opening.

This positive displacement mechanism is fundamental to how many types of pumps function, particularly in applications where a specific volume of liquid needs to be moved efficiently. In contrast, other mechanisms, like rotary pumps, are not applicable to this type of hand pump as it does not use a rotating action to move the fluid. The operation also does not depend on suction generating pressure, which is a common misconception, and it is not relying on gravity to feed liquids, as it actively draws liquid into the cylinder rather than allowing it to flow by gravitational means.