Why does the scavenger oil system have a greater capacity than the pressure system?

The scavenger oil system has a greater capacity than the pressure system primarily to compensate for oil expansion and air. In a turbine engine, as oil circulates and is subjected to varying temperatures and pressures, it expands. Additionally, the oil may become aerated due to the presence of air bubbles, which can result from turbulence within the system.

The scavenger oil system is designed to collect the returning oil from various components of the engine, typically from the bearing sumps, and direct it back to the oil tank. This system must accommodate both the increased volume of oil that results from thermal expansion and the additional volume caused by entrained air. By having a greater capacity, the scavenger system ensures that all returned oil can be effectively processed without overflowing or causing cavitation within the pump system, thereby maintaining proper oil flow and lubrication throughout the engine.

This design consideration supports optimal operation, enhancing reliability and longevity of engine components. Other options, while relevant in their own contexts, do not account for the specific need to manage the increased oil volume from expansion and air accumulation within the scavenger system.