The barrels are directly driven by the shaft. Therefore a kind of homokinetic joint is introduced on both sides. The driving torque for the barrels is limited to some friction and inertia forces. There is no hydraulic power supplied to or taken by the barrels. The conversion from hydraulic power to mechanical power (or vice versa) occurs directly in the cylinders.
The relative movement between the cylinder cups and the barrel plate is small, much smaller than for instance between a slipper and the swash plate in case of an in-line pump. This is important for wear reduction and friction losses.