Why should synthetic hydraulic fluid be stored in an airtight container?

Synthetic hydraulic fluid should be stored in an airtight container primarily to avoid atmospheric moisture contamination. Synthetic hydraulic fluids can absorb moisture from the air, which can lead to a decrease in the fluid's performance characteristics, such as its lubricating properties and thermal stability. Contamination by moisture can also promote corrosion of system components and create sludge in the fluid over time, potentially leading to system failures. Storing the fluid in an airtight container effectively minimizes exposure to moisture and helps maintain its integrity and performance.

While the other factors mentioned may be relevant in different contexts, moisture control is the most critical reason for airtight storage, as it directly impacts the fluid's operational reliability and lifespan.