Hydraulic pump life cut short by particle contamination

I was recently asked to conduct failure analysis on a hydraulic pump that had an expected service life of 10,000 hours. But the pump had been removed from its machine after achieving only 2000 hours in service.

Analysis revealed that this hydraulic pump hadn't actually failed - it had been 'worn-out' through erosive wear caused by contaminated hydraulic oil.

What is 'contaminated hydraulic oil'?

Contaminants of hydraulic oil include hard and soft particles, air, water, heat or any other matter that impairs the function of the fluid.

How does contamination affect a hydraulic pump?

Particle contamination accelerates wear of hydraulic components. The rate at which damage occurs is dependent on the internal clearance of the components within the system, the size and quantity of particles present in the oil, and system pressure.

Particles larger than the component's internal clearances are not necessarily dangerous. Particles the same size as the internal clearances cause damage through friction. However, the most dangerous particles in the long ran are those that are smaller than the component's internal clearances.

Particles smaller than 5 microns are highly abrasive. If present in sufficient quantities, these invisible 'silt' particles cause rapid wear, destroying hydraulic pumps and other components.

How can this type of hydraulic pump failure be prevented?

While the type of failure described above is unusual in a properly designed hydraulic system that is correctly maintained, this example highlights the importance of monitoring hydraulic fluid cleanliness levels at regular intervals.

As in this case, if the high levels of silt particles present in the hydraulic fluid had been identified and the problem rectified early enough, the destruction of this hydraulic pump and the significant expense of its repair could have been avoided.

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