A repairer rebuilt a hydraulic piston pump. A week later it came back like a boomerang, the subject of a warranty claim. Upon tear down the piston retaining plate was found to be broken–see inset pic. Fearing the aftermarket parts they used were not up to scratch, the repair shop quietly accepted warranty and rebuilt the pump for a second time–using genuine parts.
About a week later the boomerang came back (again!). Similar mode of failure: cracked/buckled piston retaining plate. Can’t blame the gray parts this time. Since this type of damage is consistent with high case pressure–see page 18 of Preventing Hydraulic Failures, the repairer now points the finger at the machine owner, suspecting a restricted case drain line.… continue reading »
In chapter 13 of 
Cavitation is the term used to describe the formation of gas cavities within a liquid. In a hydraulic system, this is normally taken to mean formation of vapor bubbles within the oil. But it can also mean dissolved air coming out of solution in the oil.