An improved open-center improved valving sub-assembly of the type used for power steering systems for motor vehicles is disclosed. In particular, the improved open-center improved valving sub-assembly has a valve spool member with first and second sets of input slots and first and second sets of return slots, and a valve sleeve member with output slots and diversionary slots wherein only the output slots are coupled to a power cylinder member of a host power steering system. The output slots are linked fluidically to the first sets of input and return slots by input and return flow control orifices each comprising overlapping tangentially disposed areas therebetween. The diversionary slots are linked fluidically to the second sets of input and return slots by input and return flow selective control orifices each comprising overlapping tangentially disposed areas therebetween. The input and return flow selective control orifices are tangentially shorter in length than the input and return flow control orifices whereby corresponding sets of the input and return flow selective control orifices close before corresponding sets of the input and return flow control orifices as the valve spool member is moved rotationally with respect to the valve sleeve member.