Which statement is true about 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
• D. Positive and negative displacement

Answer: (A)

The main concept is how the pump meets the engine’s changing fuel demand. Jet engine fuel pumps are categorized by how their displacement responds to operating conditions: constant-displacement and variable-displacement.

A constant-displacement pump delivers a fixed amount of fuel per revolution. The fuel control system then regulates the flow to the engine by bypassing or shuttling excess fuel, so pressure can rise as needed but the pump’s output per revolution stays the same. This keeps the system simple and robust, but it can waste energy when demand is low or pressure needs aren’t high.

A variable-displacement pump, on the other hand, changes the amount of fuel it pumps per revolution in response to engine demand. By increasing or decreasing displacement, it helps maintain a more consistent fuel pressure and flow across a wide range of engine speeds, improving efficiency and reducing bypass losses.

The other options describe specific pump designs (like gear-type or piston-type, rotary vane or diaphragm) or use terms (positive and negative displacement) that aren’t the standard way to categorize turbine engine fuel pumps.