Abstract: The hydraulic apparatus may either be a quiet hydrostatic drive with an axial piston pump and an axial piston motor or may be a quiet pump unit formed by two axial piston pumps. In either case, the apparatus includes two rotatable cylinder blocks disposed on opposite sides of a rotationally stationary valve block and tied together by a rod which transmits forces between the two cylinder blocks so that any force tending to unseat one cylinder block from the valve block tends to seat the other cylinder block against the valve block. A resiliently yieldable sealing ring on one end portion of the rod defines a pressure chamber which receives oil at working pressure to automatically increase and decrease the axial clearance between the cylinder blocks and the valve block as the working pressure increases and decreases, respectively.