A system for processing whole blood, which is to be separated into two or more components, or a blood component that has already been separated from whole blood, comprising: a) a reusable hardware unit comprising: i. two or more container-holders (16, 24), ii. a flow path opening device (32, 34, 36) associated with at least one of said two more container holders, iii. a controller for actuating: said flow path opening device and movement of said press plates (18, 26) at a selected time; b) a disposable fluid processing circuit comprising: i. at least three containers (52, 54, 56, 58; 154, 156, 158; 254, 256, 258; 354, 356; 454, 456, 458) wherein a first one (54, 154, 254, 354, 454) of said containers contains a first part of an additive solution and a second one (56, 156, 256, 356, 456) of said containers contains a second part of an additive solution and a further one comprising a separated blood component, ii. an openable flow path (13d, 13f, 13g) joining said at least three containers (52, 54, 56, 58), and iii. a flow blocker (15a, 15b, 15c) in said openable flow path (13d, 13f, 13g) wherein the two or more container-holders (16, 24) each include a press plate (18, 26), wherein the controller is configured for movement of said press plates (18, 26) at a selected time, wherein the first and the second container (54, 56; 154, 156; 254, 256; 354, 356; 454, 456) are configured for arrangement in the two or more container holders (16, 24), such that the actuation of the flow path opening device and of the movement of the press plates is controlled by the controller to express desired volumes of the first and second container (54, 56; 154, 156; 254, 256; 354, 356; 454, 456) contents. a) a reusable hardware unit comprising: i. two or more container-holders (16, 24), ii. a flow path opening device (32, 34, 36) associated with at least one of said two more container holders, iii. a controller for actuating: said flow path opening device and movement of said press plates (18, 26) at a selected time; i. two or more container-holders (16, 24), ii. a flow path opening device (32, 34, 36) associated with at least one of said two more container holders, iii. a controller for actuating: said flow path opening device and movement of said press plates (18, 26) at a selected time; b) a disposable fluid processing circuit comprising: i. at least three containers (52, 54, 56, 58; 154, 156, 158; 254, 256, 258; 354, 356; 454, 456, 458) wherein a first one (54, 154, 254, 354, 454) of said containers contains a first part of an additive solution and a second one (56, 156, 256, 356, 456) of said containers contains a second part of an additive solution and a further one comprising a separated blood component, ii. an openable flow path (13d, 13f, 13g) joining said at least three containers (52, 54, 56, 58), and iii. a flow blocker (15a, 15b, 15c) in said openable flow path (13d, 13f, 13g) wherein the two or more container-holders (16, 24) each include a press plate (18, 26), wherein the controller is configured for movement of said press plates (18, 26) at a selected time, wherein the first and the second container (54, 56; 154, 156; 254, 256; 354, 356; 454, 456) are configured for arrangement in the two or more container holders (16, 24), such that the actuation of the flow path opening device and of the movement of the press plates is controlled by the controller to express desired volumes of the first and second container (54, 56; 154, 156; 254, 256; 354, 356; 454, 456) contents. i. at least three containers (52, 54, 56, 58; 154, 156, 158; 254, 256, 258; 354, 356; 454, 456, 458) wherein a first one (54, 154, 254, 354, 454) of said containers contains a first part of an additive solution and a second one (56, 156, 256, 356, 456) of said containers contains a second part of an additive solution and a further one comprising a separated blood component, ii. an openable flow path (13d, 13f, 13g) joining said at least three containers (52, 54, 56, 58), and iii. a flow blocker (15a, 15b, 15c) in said openable flow path (13d, 13f, 13g)