External contamination is introduced by either the enviroment in which the system is operating or during field repairs and maintanence.

Enviromentally ingressed

Reservoir breathers, cylinder rod seals and pump shaft seals are the most common areas where air, water and particulates can infiltrate a system.

Prevention

• Repair leaky shaft seals and cylinder rod seals
• Excercise caution when pressure washing around reservoir breathers and filler caps

Induced during maintenance and repairs

System maintanence, component removal and replacement, component overhauls and fluid changes all present opportunities for contaminants to be introduced into a system.

Prevention

• Avoid unnecessary component removal/replacement while troubleshooting
• Avoid leaving system open to the environment for a lengthy period of time