Which statement describes a fixed displacement pump?

• A. Discharges a constant amount per revolution
• B. Discharges variable amount per revolution
• C. Only used in fuel injection systems
• D. Discharges a constant volume at high temperature

Answer: (A)

A fixed displacement pump moves the same amount of fluid with each turn of the pump. At a given RPM, this means the output flow is essentially constant because the volume moved per revolution doesn’t change, even if the system pressure varies (within the pump’s design limits). That’s why the statement describing it as discharging a constant amount per revolution is the correct one.

The idea of discharging a variable amount per revolution would belong to a variable displacement pump, where the output changes with pressure or load. Saying it’s only used in fuel injection systems isn’t accurate, since fixed displacement pumps are common in many hydraulic and fuel systems, not just injection. The notion of discharging a constant volume at high temperature isn’t the defining trait either—the displacement per revolution is fixed, but temperature mainly affects fluid density and how mass flow responds in the system, not the basic per-revolution volume.