hose reel valve

Understanding & Avoiding Hydraulic Failures Due To Contamination

Over 85% of all hydraulic system failures are caused by fluid contamination – Hydraulic fluid can be contaminated by a range of pollutants such as solids or liquids, and in fact the most common contaminant is water. If the hydraulic fluid in your system has been contaminated it can cause the hydraulics performance to decrease and result in increased component wear/damage – this can even continue after you fix the contamination if it was a long-standing issue.

In order to prevent this problem from occurring in your hydraulic systems it is important to keep your system clean. The main areas you need to consider when trying to keep your system clean (or troubleshooting contamination issues) are:

  • Internally Generated. Debris can be caused by the internal parts of the system colliding – if parts are ill fitted, old or wearing this can cause issues.
  • Built-In. Contamination could already be there from dirty valves or oil.
  • Servicing, repairs and replacement of parts in the field can introduce foreign matter into the hydraulics.
  • Contamination entering through malfunctioning cylinder rod seals and reservoir breathers.
  • Hose Assembly. Rubber and metal particles introduced into the system from the assembly of hoses.
  • Restrictions on the pump inlet, like a suction strainer or suction hose that’s too small, an over speeding pump or oil that’s too hot or cold.
  • Leaking fittings, low oil level, incorrect (or lack of) tank baffles.

We recommend that all systems have an ISO 4406 cleanliness code of 19/14/11, to indicate particle levels:

19 = No more than 2500 to 5000 particles greater or equal to 4 microns.
14 = No more than 80 to 160 particles greater or equal to 6 microns.
11 = No more than 10 to 20 particles greater or equal to 14 microns.

Many people find it difficult to achieve or maintain the cleanliness or their oil.  If this is the case try asking these questions:

  • How clean is the oil from your supplier?
  • What is their cleanliness code?
  • Have you run new oil through a filtration cart before filling or topping up your Hydraulic system?

Along with stringent checks and maintenance, you could use contamination monitoring systems to examine the oil.  These can be an integral part of the system, jamsconstantly monitoring or performed manually as part of your maintenance program.  Hydraulic oil is expensive and the norm is to just replace it according to the instructions from the manufacturer.  A simple test could save you thousands each year in unnecessary replacement costs.   Consider Proactive maintenance instead of Preventative maintenance!

  • High pressure system filter of 10 microns or less following the pump outlet.
  • Low pressure return line filter of 10 micros just before the reservoir.
  • Reservoir desiccant top mount breathers.


Hydraulic systems can be incredibly efficient and powerful systems – keeping on top of fluid cleanliness is well worth the time and effort so put regular checks in place and go through the above points to help you get the most out of your equipment.