The pressure pot must be filled with the proper type of hydraulic fluid.

• A. Mineral oil
• B. Hydraulic fluid
• C. Silicone oil
• D. Brake fluid

Answer: (B)

The pressure pot is part of the aircraft’s hydraulic system, so it must contain the same hydraulic fluid the system is designed to use. The fluid’s viscosity, lubricating properties, and chemical compatibility with seals, hoses, and metals determine how well the pot pressurizes and delivers fluid to the actuators. Using the correct hydraulic fluid ensures seals don’t swell or degrade, keeps the system free of incompatible reactions, and preserves predictable pressure and performance.

Brake fluid is glycol-based and hygroscopic, which can damage elastomers and alter fluid properties; silicone oil and mineral oil have different characteristics and are not typically approved for the system. Mixing fluids or using an unapproved fluid can lead to leaks, wear, or failure of components. Therefore, the pressure pot must be filled with the approved hydraulic fluid specified for the system.