Recently I came across a medium sized offshore HPU on a ship that was badly damaged through overheating. Apparently the oil temperature reached temperatures of over 150 degrees Celsius. The seals in many hydraulic components are typically not suitable for temperatures much greater than 80 degrees Celsius. The ship owner had to replace the main pumps and valves, a time consuming and very costly operation. Failure of a temperature switch led to the system overheating. It didn’t help that the cooling water to the oil / water cooler was switched off.
The failure reminded me of a similar costly overhaul of a hydraulic system on a mobile drilling rig. On that particular rig the pump suction valves were incorrectly ordered with EPDM rather that NBR seals. EPDM seals are more suitable for use with water valves. Over time the EPDM seals disintegrated by being in contact with hydraulic oil. Bits of EPDM rubber migrated throughout the whole hydraulic system and led to the catastrophic failure of pumps, motors and valves.
These two examples show how careful component selection and proper operating procedures are critical to ensure reasonable service life of hydraulic systems and components. The cost of repairs in both situations amounted to tens of thousands of dollars.