Which description best classifies the attached LO pump?

• A. Vertical mounted; centrifugal; piston
• B. Vertical mounted; positive displacement; rotary vane
• C. Horizontal mounted; positive displacement; rotary screw
• D. Horizontal mounted; centrifugal; piston

Answer: (C)

This question tests how to classify a lubricating oil pump by orientation, displacement type, and rotor design. For lubrication systems, a steady, pressurized flow of viscous oil is needed, so a positive displacement pump is favored because its flow remains relatively constant as system pressure changes. Within positive displacement pumps, a rotary screw design uses two intermeshing screws to trap fixed volumes of oil and move them along with minimal pulsation, which is ideal for lubricating circuits dealing with viscous fluids and varying speeds.

The horizontal mounting matches common installation practice for oil pumps that are driven by the engine’s accessory drive and tied into long piping runs, making alignment and service straightforward. Centrifugal pumps, on the other hand, rely on head pressure and produce flow that varies with system pressure, which isn’t suited for maintaining consistent lubrication. Piston and rotary vane pumps are other positive displacement options, but they don’t fit the typical LO pump configuration shown in many gas turbine installations, whereas a rotary screw pump does.

So the best match is a horizontally mounted, positive displacement, rotary screw pump.