Apparatus for liquid exchanging a biomolecule-containing liquid comprising: a) a first multiple inlet flow-controller and a first tangential flow filtration device, the first multiple-inlet flow controller comprising: i) a first inlet for a first liquid medium comprising a biomolecule comprising an intermittent-flow inlet valve which prevents flow in a first position but permits flow in at least a second position; ii) at least a second inlet for a second liquid medium comprising an intermittent-flow inlet valve which prevents flow in a first position but permits flow in at least a second position; iii) an outlet in fluid connection with the first tangential flow filtration device; and iv) a programmable control unit to regulate the opening and closing through at least 10 cycles of the intermittent-flow inlet valves such that in operation, only one valve is open at any given time in order to achieve the required relative quantities of the input liquids flowing through the multiple-inlet flow controller and with a predetermined time period or cycle rate according to the required proportion of the cycle time to generate a desired composition; b) a second multiple inlet flow-controller and a second tangential flow filtration device, the second multiple-inlet flow controller comprising: i) a first inlet being in fluid connection with the retentate from the first tangential flow filtration device; ii) at least a second inlet for a third liquid medium; and iii) an outlet in fluid connection with the second tangential flow filtration device; and c) a means for imparting flow of the liquids through the flow-controllers and the tangential flow filtration devices. a) a first multiple inlet flow-controller and a first tangential flow filtration device, the first multiple-inlet flow controller comprising: i) a first inlet for a first liquid medium comprising a biomolecule comprising an intermittent-flow inlet valve which prevents flow in a first position but permits flow in at least a second position; ii) at least a second inlet for a second liquid medium comprising an intermittent-flow inlet valve which prevents flow in a first position but permits flow in at least a second position; iii) an outlet in fluid connection with the first tangential flow filtration device; and iv) a programmable control unit to regulate the opening and closing through at least 10 cycles of the intermittent-flow inlet valves such that in operation, only one valve is open at any given time in order to achieve the required relative quantities of the input liquids flowing through the multiple-inlet flow controller and with a predetermined time period or cycle rate according to the required proportion of the cycle time to generate a desired composition; i) a first inlet for a first liquid medium comprising a biomolecule comprising an intermittent-flow inlet valve which prevents flow in a first position but permits flow in at least a second position; ii) at least a second inlet for a second liquid medium comprising an intermittent-flow inlet valve which prevents flow in a first position but permits flow in at least a second position; iii) an outlet in fluid connection with the first tangential flow filtration device; and iv) a programmable control unit to regulate the opening and closing through at least 10 cycles of the intermittent-flow inlet valves such that in operation, only one valve is open at any given time in order to achieve the required relative quantities of the input liquids flowing through the multiple-inlet flow controller and with a predetermined time period or cycle rate according to the required proportion of the cycle time to generate a desired composition; b) a second multiple inlet flow-controller and a second tangential flow filtration device, the second multiple-inlet flow controller comprising: i) a first inlet being in fluid connection with the retentate from the first tangential flow filtration device; ii) at least a second inlet for a third liquid medium; and iii) an outlet in fluid connection with the second tangential flow filtration device; and i) a first inlet being in fluid connection with the retentate from the first tangential flow filtration device; ii) at least a second inlet for a third liquid medium; and iii) an outlet in fluid connection with the second tangential flow filtration device; and c) a means for imparting flow of the liquids through the flow-controllers and the tangential flow filtration devices.