Programmable, fluid pressure actuated blood processing systems and methods are used in association a blood separation device. The systems and methods employ a cassette, which contains several preformed, pneumatically actuated pump stations, several preformed fluid flow paths, and several preformed, pneumatically actuated valves in the fluid flow paths. The systems and methods also employ a programmable pneumatic actuator to hold the cassette and selectively apply pneumatic force to the valves and pump stations.