What methods are used to pressurize hydraulic reservoirs?

Pressurizing hydraulic reservoirs is commonly achieved by using air pressure, which is often sourced from the aircraft cabin or through an aspirator mechanism. This method ensures that the hydraulic fluid is adequately pressurized to maintain proper system functionality and efficiency. By using cabin air pressure, the system can stay maintain the required fluid level in the reservoir while also accommodating changes in fluid volume due to temperature variations and system operation.

Utilizing an aspirator works on the principle that as the aircraft moves, it creates a low-pressure area that can draw air into the reservoir, effectively pressurizing the hydraulic fluid within. This is particularly advantageous because it uses ambient conditions created during flight operations, making it efficient and reliable.

Other methods such as using only an electric pump, hydraulic fluid from the main system, or mechanical pumps have limitations. An electric pump may not always be reliable or present in all systems, while relying strictly on hydraulic fluid from the main system may lead to pressure inconsistencies under varying operating conditions. Exclusive use of mechanical pumps may also restrict versatility and depend on engine power. Thus, the method of using air pressure from the cabin or aspirator stands out as a practical and efficient approach for maintaining hydraulic reservoir pressure.