Failure of a Piston Pump

I was asked recently to give a second opinion on the cause of failure of an axial piston pump. The hydraulic pump had failed after a short period in service and my client had pursued a warranty claim with the manufacturer. The manufacturer rejected the warranty claim on the basis that the failure had been caused by contamination of the hydraulic fluid. The foundation for this assessment was scoring damage to the valve plate (Figure 1).

How does contamination cause this type of damage to a hydraulic pump?

When hydraulic fluid is contaminated with hard particles that are the same size as the clearance between two lubricated surfaces, a process known as three body abrasion occurs. Three-body abrasion results in scoring and heavy wear of sliding surfaces (Figure 2).