Closed system and methods for mixing additive solutions while removing undesired matter from blood cells

A blood processing system comprising

• a first variable volume chamber to hold blood,
• a second variable volume chamber to hold additive solution for blood,
• a separation device to remove undesired material from blood,
• an actuated element to exert force simultaneously upon both first and second variable volume chambers to simultaneously expel a first flow of blood from the first variable volume chamber and a second flow of additive solution from the second variable volume chamber, and
• a fluid flow system to convey fluid flow in response to force exerted by the actuated element and without application of a force external to the actuated element, the fluid flow system including a first branch communicating with the first variable volume chamber to convey the first flow of blood at a first rate, a second branch communicating with the second variable volume chamber to convey the second flow of additive solution at a second rate different than the first rate, the second flow being simultaneous with and independent of the first flow, means for establishing a desired ratio between the first rate and the second rate, and a third branch communicating with the first and second branches to mix outside the first and second variable volume chambers the blood from the first branch with the additive solution from the second branch to create a mixed flow comprising blood and additive solution, the third branch further communicating with the separation device to direct the mixed flow of blood and additive solution through the separation device.