Why are some hydraulic reservoirs pressurized?

Pressurizing hydraulic reservoirs serves the primary purpose of ensuring that there is a consistent and positive flow of hydraulic fluid to the engine-driven pump, especially at high altitudes where atmospheric pressure is lower. This is critical because hydraulic systems rely on fluid pressure to operate effectively, and any loss of pressure can lead to reduced system performance or even failure of hydraulic components.

At higher altitudes, unpressurized fluid may not flow adequately due to the drop in atmospheric pressure, which can lead to cavitation or vapor lock in the system. By pressurizing the reservoir, the hydraulic fluid's density and flow characteristics are maintained, thereby allowing for reliable operation of the hydraulic systems under varying atmospheric conditions.

While other factors such as preventing overheating, enhancing component longevity, and regulating temperature in the hydraulic fluid are certainly important considerations in hydraulic systems, they do not directly relate to the primary reason for pressurizing the reservoir. Thus, ensuring positive flow to the pump is the most critical function that pressurization achieves in the context of high altitude operations.