Here you have a good old Sauer Danfoss series 90 closed loop pump,
which got so worn, that the brass part of the barrel disappeared completely! I
don't know the story of this particular pump, but it made me remember a
troubleshooting episode I participated a couple of years ago, which
involved an alike series 90 with a similar type of damage.
If you look at the last two pictures (I apologize
for the quality - these were taken by my cell), you will see a pump,
which got the same king of damage, but was still able to deliver usable flow
at 400 bars (with the charge pressure falling to around 16 bars at that
point) - I personally was involved in the troubleshooting of the
machine (small agricultural vehicle), and I guarantee that 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 circuit 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!!!