Which statement is true about engine-driven fuel pumps according to the material?

Which statement is true about engine-driven fuel pumps according to the material?

• A. They must be electric
• B. They are always positive displacement
• C. They are either nonconstant displacement or nonpositive displacement
• D. They have a fixed flow rate

Answer: (C)

Engine-driven fuel pumps don’t always deliver a fixed amount of fuel per unit time. They can be either variable-displacement pumps, where the volume they move per revolution changes with conditions, or dynamic (centrifugal) types, where the flow is determined by the head against which they must pump and isn’t set by a fixed displacement. That’s why the statement that describes them as either nonconstant displacement or nonpositive displacement is true: one part covers pumps whose displacement isn’t constant, and the other covers pumps that don’t rely on a fixed positive displacement to produce flow. This also explains why other statements aren’t correct. They aren’t necessarily electric—engine-driven implies mechanical drive from the engine itself, not an electric motor. They aren’t always positive-displacement pumps, since dynamic/centrifugal types fall into the nonpositive-displacement category. And they don’t have a fixed flow rate, because flow can vary with engine speed and system pressure.

Engine-driven fuel pumps don’t always deliver a fixed amount of fuel per unit time. They can be either variable-displacement pumps, where the volume they move per revolution changes with conditions, or dynamic (centrifugal) types, where the flow is determined by the head against which they must pump and isn’t set by a fixed displacement. That’s why the statement that describes them as either nonconstant displacement or nonpositive displacement is true: one part covers pumps whose displacement isn’t constant, and the other covers pumps that don’t rely on a fixed positive displacement to produce flow.

This also explains why other statements aren’t correct. They aren’t necessarily electric—engine-driven implies mechanical drive from the engine itself, not an electric motor. They aren’t always positive-displacement pumps, since dynamic/centrifugal types fall into the nonpositive-displacement category. And they don’t have a fixed flow rate, because flow can vary with engine speed and system pressure.