Tronair HPU preventative maintenance

Hydraulic power units are key pieces of equipment for maintaining aircraft. Many fixed base operations and maintenance repair and overhaul providers struggle to troubleshoot hydraulic power unit maintenance issues. Repairs on these units can be time-consuming and costly, especially for aviation maintenance personnel that seldom perform HPU repairs. Equipment manufacturers have found that the majority of HPU issues arise from improper maintenance. Proper HPU preventative maintenance techniques can extend useful equipment life and reduce issues. This overview will provide you with what you need to know to keep your HPU running smoothly for years to come.

HPU Hydraulic Fluid Care

Inspect hydraulic fluid at regular intervals, typically every C check (20 – 24 months) to ensure normal color and smell. If the color varies, the fluid appears to have visible contaminants, or the smell seems strange, the fluid may have deteriorated. Deterioration in this scenario can be caused by contamination, oxidation, or thermal degradation. To check if the hydraulic fluid is in normal working condition, perform a sample analysis.


The most common type of contamination is dirt and debris. These contaminants can cause excessive wear and increase the oxidation rate.


The most common cause of degradation is oxidation. Oxidation occurs from increased temperature, pressure, and speed of hydraulic machines. When this happens, hydraulic fluid takes on a sludge-like viscosity. Temperatures over 203 Fahrenheit (95 Celsius) can cause oxidation. Check for any points where the fluid can come into contact with air.

Thermal Degradation

Thermal degradation refers to the separation of carbon bonds when extreme heat is added to hydraulic fluid’s maximum temperature. This process occurs when temperatures are over 572 degrees Fahrenheit (300 degrees Celsius). To reduce the occurrence of thermal degradation, allow enough time for equipment start-up and shut-down. Hydraulic fluid performs when temperature changes are gradual. During machine shut-down, it is possible for fluid to become trapped in the heater and experience excess heat exposure.Consider Tronair GSE training to educate AMTs, resulting in better equipment maintenance. Contact the experts at e2b calibration, a Tronair Authorized Service Center. Reach out HERE or via email at [email protected]