A fluid processing system comprising: a disposable fluid circuit comprising: a separation chamber; at least one plungerless syringe, the syringe comprising a wall defining a barrel having a first end and a second end, the barrel having a bore without a plunger disposed therein, and at least one capacitive sensor disposed on an outer surface of the wall of the syringe; and a flow control cassette comprising a housing containing a plurality of separate channels (230, 232, 234, 236, 238, 240, 242, 244, 246, 248, 250, 252, 254, 256, 258, 260) connected to a plurality of selectable junctions, at least one of the plurality of separate channels connected to the first end of the barrel of the at least one plungerless syringe; and reusable hardware configured to accept the disposable fluid circuit and comprising: a separator connected to the separation chamber; at least one syringe pump (142, 144), the second end of the barrel of the at least one syringe coupled to the at least one syringe pump (142, 144), the at least one syringe pump (142, 144) configured to draw fluid into and push fluid from the at least one syringe; a control cassette interface having at least one actuator for each of the selectable junctions and a coupling connected to the at least one capacitive sensor; and at least one controller coupled to the separator, the at least one syringe pump (142, 144) and the control cassette interface, the controller configured to selectively operate the separator, the at least one syringe pump and the interface to provide a procedure according to a protocol. a disposable fluid circuit comprising: a separation chamber; at least one plungerless syringe, the syringe comprising a wall defining a barrel having a first end and a second end, the barrel having a bore without a plunger disposed therein, and at least one capacitive sensor disposed on an outer surface of the wall of the syringe; and a flow control cassette comprising a housing containing a plurality of separate channels (230, 232, 234, 236, 238, 240, 242, 244, 246, 248, 250, 252, 254, 256, 258, 260) connected to a plurality of selectable junctions, at least one of the plurality of separate channels connected to the first end of the barrel of the at least one plungerless syringe; and a separation chamber; at least one plungerless syringe, the syringe comprising a wall defining a barrel having a first end and a second end, the barrel having a bore without a plunger disposed therein, and at least one capacitive sensor disposed on an outer surface of the wall of the syringe; and a flow control cassette comprising a housing containing a plurality of separate channels (230, 232, 234, 236, 238, 240, 242, 244, 246, 248, 250, 252, 254, 256, 258, 260) connected to a plurality of selectable junctions, at least one of the plurality of separate channels connected to the first end of the barrel of the at least one plungerless syringe; and reusable hardware configured to accept the disposable fluid circuit and comprising: a separator connected to the separation chamber; at least one syringe pump (142, 144), the second end of the barrel of the at least one syringe coupled to the at least one syringe pump (142, 144), the at least one syringe pump (142, 144) configured to draw fluid into and push fluid from the at least one syringe; a control cassette interface having at least one actuator for each of the selectable junctions and a coupling connected to the at least one capacitive sensor; and at least one controller coupled to the separator, the at least one syringe pump (142, 144) and the control cassette interface, the controller configured to selectively operate the separator, the at least one syringe pump and the interface to provide a procedure according to a protocol. a separator connected to the separation chamber; at least one syringe pump (142, 144), the second end of the barrel of the at least one syringe coupled to the at least one syringe pump (142, 144), the at least one syringe pump (142, 144) configured to draw fluid into and push fluid from the at least one syringe; a control cassette interface having at least one actuator for each of the selectable junctions and a coupling connected to the at least one capacitive sensor; and at least one controller coupled to the separator, the at least one syringe pump (142, 144) and the control cassette interface, the controller configured to selectively operate the separator, the at least one syringe pump and the interface to provide a procedure according to a protocol.