What are the two categories of turbine engine fuel pumps?

• A. Constant displacement and variable displacement
• B. Gear-type and piston-type
• C. Rotary vane and diaphragm pumps
• D. Positive and negative displacement

Answer: (A)

Fuel pumps in turbine engines are grouped by how their output changes with engine demand: constant-displacement and variable-displacement.

A constant-displacement pump delivers the same volume of fuel per revolution regardless of the system pressure. To keep the fuel pressure from rising with engine demands, the excess fuel is typically bypassed or regulated by valves, so the metering unit still sees the right pressure but the flow may vary if the demand changes beyond what the pump can supply.

A variable-displacement pump changes how much fuel it moves with each revolution. By adjusting its displacement, it can maintain a nearly steady discharge pressure as engine speed and fuel demand vary. This makes metering more stable and reduces the need for large bypass paths.

This classification directly describes how the pump handles flow and pressure in response to engine demand, which is why it is the best answer.