hydrostatic transmission and cavitation.

AeroTron

My knoledge in hydraulics are simply basic. At the moment I am trying to figure out what
causes cavitation in closed loop hydrostatic transmission. Im using a hydraulic simulation tool for studying.

My question, without the charge pump there is cavitation and my desired output rpm will not happen. why is it? Is it because of internal leakage? I have no clue

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