Insane Hydraulics

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Danfoss Series 90 With Missing Barrel Bronze Layer

Here you have an old Sauer Danfoss series 90 closed-loop pump which got worn-out to the point where the bronze layer of the barrel disappeared completely! I don't know the story of this particular pump, but it made me remember a troubleshooting episode that I participated in a couple of years ago, which involved a series 90 with a similar damage.

If you look at the last two pictures (I do apologize for the quality - these were taken by a very old cell phone), you will see a pump that was still able to sustain usable flow at 400 bar (with the charge pressure falling to around 16 bar at that point) - I was involved in the troubleshooting of the machine (a small agricultural vehicle), and I guarantee it's true! The rest of the circuit was OK, and the oil was at working temperature! I still can not find an explanation of how a closed loop pump, worn-out to this state (the groove in the valve plate alone was almost half a millimeter deep!), was able to produce any flow at all!!!