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    Correct evaluation of the condition of a hydraulic pump or motor parts is an important stage of an overhauling process. This is when you define which components can be re-used and which should be replaced. However, not all types of wear are evident and easily detectable, making it possible for some damaged parts to skip detection, and lead to a premature failure of an overhauled pump/motor.

    These pictures are a good example of what I call a "sneaky damage". These parts don't present any apparent, visible at first glance damage (with the exception of normal wear), but under a closer inspection appear to be damaged beyond repair. Take this cylinder block, for example, which is from a Komatsu open circuit pump from a PC-340 excavator. Upon inspecting the respective swashplate, pistons, the valve plate, and the sealing surface of the block, you will find nothing but normal particle wear, which may trick you into assuming that with a little bit of grinding and lapping the pump will be good for an extra couple of thousand hours... But if you take a flashlight and peek inside the bores, you will see that there are chunks of material missing in every single bore due to cavitation erosion, which makes the part unserviceable.

     By the way, check out the unequal pitch of the pressure ports. This is a patented Komatsu's noise reduction solution. According to Komatsuneers, it disperses the noise frequency phase, thus making the noise less harsh. I am not sure that it makes that much of a difference, but suppose it can't hurt...

    Another example. This spool is from a motion control valve mounted on a propel motor of a small excavator. You will have to look real hard to find that cavitation erosion "scooped out" a narrow but very deep (around 4 mm) pit. The spool appears to be in a good condition, but should be replaced, as pretty soon the thin wall will come to an end, and "kaboom!" - the spool is gone along with the respective housing...

    It is in human nature to assume things. It is just the way we are built. That is why it is not uncommon for a mechanic, after finding a series of parts in good condition,  to assume that the rest of  the parts of an assembly are in good condition too. In 95 percent of cases this assumption will be true, leaving the five percent for nasty making-you-look-stupid surprises.

    Some types of damage, which is especially the case with the cavitation erosion, can be concealed, and require additional attention to be found. That is why it is important to carefully evaluate every part of an assembly, without jumping into rushed assumptions and taking the parts condition for granted.
Cylinder Block, Komatsu PC340
Cylinder Block, Komatsu PC340
Cavitation erosion
Cavitation erosion
Cavitation erosion
Hydraulic valve spool
Cavitation erosion
Cavitation erosion