Learning Objectives 021.03.02.02.09: Explain the advantages and disadvantages of a high-pressure system over a low-pressure system.

Only the simplest hydraulic systems, such as the brake circuit on a light aircraft, are powered by human effort. All advanced hydraulic systems use some form of pump to increase hydraulic pressure and facilitate fluid flow under pressure. Hydraulic systems can be classified as either:

• Low-pressure systems: Typically operating up to 2000 PSI.
• High-pressure systems: Typically operating at 3000 PSI, though some aircraft may use hydraulic pressures of 4000 to 5000 PSI.

High pressure reduces fluid volume and component mass. However, even at higher pressures, hydraulic fluid is considered incompressible. Very high pressures can induce shear stresses in the fluid, leading to adverse hydraulic effects. Additionally, there is a slightly increased risk of fluid leaks at joints in the lines.