Steering wheel turned to right:

The valve piston (4) is adjusted to the right and the inlet groove (9) is open. The valve piston (5) is adjusted to the left and the inlet groove (10) is closed. This enables pressurized oil to enter the right cylinder chamber. The oil in the left cylinder chamber is forced out and flows back to the oil container.

Fig 1: Recirculating Ball Power Steering Unit - Steering Wheel Turned To Right Position (Cross Sectional View)

Courtesy of BMW OF NORTH AMERICA, INC.