Hydraulic Piston Pump Shaft Seals and Case Drain Lines

IM000260A 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 »

Hydraulic System Modifications and Machine Safety

big question markIn chapter 13 of The Hydraulic Maintenance Handbook I discuss in detail the elimination of problems by engineering them out. An obvious example of this strategy is, if a hydraulic system has tapered thread adapters, their replacement with a more reliable type of connector eliminates the possibility of recurring leaks. Job done. And if an oil to water heat exchanger isn’t used, water can never contaminate the hydraulic fluid. Or if a suction strainer is discarded, it can never clog and destroy the pump. And so on.

Importantly, none of the above types of modifications can be regarded as a ‘significant change’ to the machine.… continue reading »

20 Ways Cavitation Can Occur In a Hydraulic System

photo credit eaton vickersCavitation 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.

Cavitation erosion occurs when gas cavities in the oil collapse (implode) under pressure, in proximity to a metal surface. But in a hydraulic system, the formation of gas cavities is usually (but not always) associated with the presence of a vacuum (negative gauge pressure). And the presence of vacuum-induced, mechanical forces can be far more damaging, and catastrophically so, to hydraulic components, than pressure-induced bubble implosion.… continue reading »