Excavators as a rule spend much more time digging than they do travelling (Or at least they're supposed to) so they use open loop (not to be confused with open center, though some are, but I digress) hydraulics because that's what works best with lots of cylinders. Things that travel a lot like rubber tracked dumpers and make lots of turns like track loaders and skid steers, or need to travel faster, generally use hydrostatic drives. They're more efficient because they run higher pressures and pump the oil around in the closed loops rather than back through the tank each trip. When turning the slow side actually backfeeds power into the pump stack to help out. Open loop travel drives will have a counterbalance valve fitted which only allows the motors to turn as fast as their is oil flow for, if the motor tries to run ahead of the available oil flow, the valve spool shifts to restrict the outlet port providing a braking effect. Hydrostats generally only brake by backfeeding into the engine.
So, there ya are, travel systems 101 Lantrax style, LOL
