A renal therapy system (10, 110, 210, 300, 310, 400, 410, 500, 510, 610, 710, 810, 910, 950) comprising: a dialyzer (20, 30); a balancing system (340, 360, 516, 552, 572, 591, 644, 652, 676, 680, 700, 743, 754) configured to equalize flow volume of renal failure therapy fluid to the dialyzer and from the dialyzer, the balancing system including a fresh renal therapy fluid side (344, 362) and a spent renal therapy fluid side (342, 364); a fresh renal therapy fluid pressure sensor (46, 404, 406, 412, 422, 424, 428, 432, 436, 509, 709, 745, 747) positioned and arranged to detect a pressure of fresh renal failure therapy fluid on the fresh renal therapy fluid side of the balancing system; a spent renal therapy fluid pressure sensor (46, 402, 406, 416, 422, 424, 428, 432, 436, 509, 709, 745, 747) positioned and arranged to detect a pressure of spent renal failure therapy fluid on the spent renal therapy fluid side of the balancing system; and a controller configured to (i) receive a signal from the fresh and spent renal therapy fluid pressure sensors indicative of the detected pressures of the fresh and spent renal failure therapy fluids, respectively, and (ii) control the flow of fresh renal failure therapy fluid and the flow of spent renal failure therapy fluid for the balancing system so that (a) a pressure of the fresh renal failure therapy fluid to the balancing system is equal to a pressure of the spent renal failure therapy fluid to the balancing system, or (b) a pressure of the fresh renal failure therapy fluid from the balancing system is equal to a pressure of the spent renal failure therapy fluid from the balancing system. a dialyzer (20, 30); a balancing system (340, 360, 516, 552, 572, 591, 644, 652, 676, 680, 700, 743, 754) configured to equalize flow volume of renal failure therapy fluid to the dialyzer and from the dialyzer, the balancing system including a fresh renal therapy fluid side (344, 362) and a spent renal therapy fluid side (342, 364); a fresh renal therapy fluid pressure sensor (46, 404, 406, 412, 422, 424, 428, 432, 436, 509, 709, 745, 747) positioned and arranged to detect a pressure of fresh renal failure therapy fluid on the fresh renal therapy fluid side of the balancing system; a spent renal therapy fluid pressure sensor (46, 402, 406, 416, 422, 424, 428, 432, 436, 509, 709, 745, 747) positioned and arranged to detect a pressure of spent renal failure therapy fluid on the spent renal therapy fluid side of the balancing system; and a controller configured to (i) receive a signal from the fresh and spent renal therapy fluid pressure sensors indicative of the detected pressures of the fresh and spent renal failure therapy fluids, respectively, and (ii) control the flow of fresh renal failure therapy fluid and the flow of spent renal failure therapy fluid for the balancing system so that (a) a pressure of the fresh renal failure therapy fluid to the balancing system is equal to a pressure of the spent renal failure therapy fluid to the balancing system, or (b) a pressure of the fresh renal failure therapy fluid from the balancing system is equal to a pressure of the spent renal failure therapy fluid from the balancing system.