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    Despite of the fact that the main purpose of a charge pump in a closed loop is to keep the circuit filled and to provide servo pressure, there are still some people who are, for some reason, convinced that the higher the charge pressure, the better is the machine's performance. On these pics you can see a charge pump from an old A4V (Hydromatik), the pump had been in a perfect condition a week before the pics were taken. The client claimed warranty and  said the machine was running OK and then stopped suddenly (gee, I wonder why?). However a closer inspection revealed a COMPLETELY BLOCKED charge pressure valve, and it was not damaged, it had been blocked on purpose, by screwing in the regulating screw till it stopped. Sorry, guys, no warranty here. I can only guess how high the charge pressure went...

    These internal gear pumps are not hydrostatically balanced, which means the pressure inside the pump pushes the outer ring  towards the housing and the central gear in the opposite direction, creating lateral load on the bushings. There is no need to balance these pumps as their working pressure is relatively low. However if the pressure goes beyond certain level, the disbalance will cause excessive wear both of the bushings and the housing (especially the housing). On the pics you see that the outer gear-ring "machined" through the housing as far as the o'ring cavity before going "kaboom". This type of wear and the fact the charge pressure relief was "blocked"  left no doubts as for why the failure happened.

    Don't try this at home!