This type of pump uses a piston in a reciprocating motion and is commonly used for pumping sludges.

• A. Positive displacement piston pump
• B. Centrifugal pump
• C. Diaphragm pump
• D. Gear pump

Answer: (A)

A piston-driven positive-displacement pump traps a fixed volume of sludge with each back-and-forth stroke and then pushes that exact amount out on the forward stroke. That reciprocating motion is ideal for thick, particulate-laden fluids because it delivers high pressure and can handle viscous sludges without relying on an impeller, which can clog or lose efficiency with solids. The mechanism ensures a predictable, controlled flow even when the fluid is not easy to move.

Centrifugal pumps rely on high-speed impellers to move fluid dynamically, so their output drops with higher viscosity and solids content, making them less suitable for sludge with grit or fibers. Diaphragm pumps use a flexible membrane to create volume changes and can handle sludges, but the mechanism described here specifically involves a piston. Gear pumps are rotary and move fluid via intermeshing gears, not by a reciprocating piston.