If engine demand increases, which pump type adjusts discharge accordingly?

• A. Fixed displacement pump
• B. Variable displacement pump
• C. Gear pump
• D. Piston pump

Answer: (B)

When engine demand rises, the pump that can actively change how much fluid it moves per revolution is needed. A variable displacement pump does exactly that: it adjusts its displacement in response to control signals or pressure feedback, so the discharge increases as demand grows and decreases when demand drops. This keeps flow matched to what the engine needs and helps control system pressure and efficiency.

Fixed displacement pumps, by contrast, push out the same amount of fluid per revolution regardless of demand. So if the engine suddenly needs more flow, the system may experience pressure spikes or underfueling.

Gear pumps are typically fixed displacement, delivering a constant flow per turn. Piston pumps can be either fixed or variable, but the type designed to adapt to demand is the variable displacement variant, which is why it best fits a scenario where discharge needs to adjust with engine demand.