The effect of dirty hydraulic oil on cylinders, the ISO 4406 cleanliness standard, and filtration methods.
Oil Quality and Failures
Approximately 80% of industrial hydraulic system failures are caused by dirty or degraded hydraulic oil. Particle contamination causes scoring on piston surfaces, blockage in valves, and shortened gasket life.
Hydraulic oil should be analysed regularly for viscosity, acid number (TAN), water content, and particle count.
ISO 4406 Cleanliness Standard
The ISO 4406 standard numerically classifies particle contamination in hydraulic oil. A cleanliness class of 18/16/13 or better should be targeted in industrial hydraulic systems.
Even new oil can be contaminated during tanker filling; therefore, filtration before filling is essential. Off-line filtration units are an effective method for maintaining oil cleanliness while the system is running.
Filtration Applications
Pressure line, return line, and suction line filters should be replaced at regular intervals. Clogging indicators must be monitored and filter bypass conditions avoided.
During cylinder maintenance, system oil should be checked and, if necessary, complete oil change and tank cleaning should be performed.
