Some examples of commutating valves are the valves in geroter motors and valves in radial piston motors. These valves connect the pressure and tank ports at the correct time. Some are radial seal and some are face seal designs. The face seal can take up some wear if pressure balanced, but can be a problem if quick pressure changes occur. Radial valves require a close tolerance fit between the two parts. Both types require accurate location of the ports and will not tolerate contamination.