Balancing device (41, 410, 81, 91) for balancing between an inflow into a blood treatment unit of a medical treatment device and an outflow out of the blood treatment unit, with a balancing unit which has at least one exchange vessel, a first inlet line leading to the exchange vessel, for feeding liquid from a liquid source into the exchange vessel, and a first outflow line issuing from the exchange vessel, for discharging the liquid from the exchange vessel into a drain, a second outflow line issuing from the exchange vessel, for discharging liquid from the exchange vessel into the treatment unit, and a second inlet line leading to the exchange vessel, for feeding liquid from the treatment unit into the exchange vessel, means (21, 22, 72) for conveying liquid into and/or out of the exchange vessel, and means (30, 17) for interrupting the inflow of liquid into the exchange vessel through the first and through the second inlet line and/or means (16, 12) for interrupting the outflow of liquid out of the exchange vessel through the first and through the second outflow line, a control unit for controlling the means (21, 22, 72) for conveying liquid and the means (16, 12, 30, 17) for interrupting the inflow and/or outflow of liquid, wherein the control unit is designed in such a way that, in a first work cycle of successive work cycles, a first fluid circulation is formed in which spent liquid from the exchange vessel flows into the drain and is replaced by fresh liquid from the liquid source and, in a second work cycle of the successive work cycles, a second fluid circulation is formed in which fresh liquid from the exchange vessel flows into the treatment unit and is replaced by spent liquid from the treatment unit, and characterized by a pressure detector, connected to the control unit, for detecting the pressure in the exchange vessel during the first work cycle, the second work cycle and a third work cycle, and wherein the control unit is further designed to shut off the first and the second outflow line in the third work cycle, and the pressure in the exchange vessel is brought to a previously measured pressure, wherein the previously measured pressure corresponds to the higher of the pressures in the exchange vessel during the first work cycle and during the second work cycle, or to shut off the first and the second inlet line in the third work cycle, and the pressure in the exchange vessel is brought at the outlet side to a previously measured pressure, wherein the previously measured pressure corresponds to the lower of the pressures in the exchange vessel during the first work cycle and during the second work cycle. a first inlet line leading to the exchange vessel, for feeding liquid from a liquid source into the exchange vessel, and a first outflow line issuing from the exchange vessel, for discharging the liquid from the exchange vessel into a drain, a second outflow line issuing from the exchange vessel, for discharging liquid from the exchange vessel into the treatment unit, and a second inlet line leading to the exchange vessel, for feeding liquid from the treatment unit into the exchange vessel, means (21, 22, 72) for conveying liquid into and/or out of the exchange vessel, and means (30, 17) for interrupting the inflow of liquid into the exchange vessel through the first and through the second inlet line and/or means (16, 12) for interrupting the outflow of liquid out of the exchange vessel through the first and through the second outflow line, a control unit for controlling the means (21, 22, 72) for conveying liquid and the means (16, 12, 30, 17) for interrupting the inflow and/or outflow of liquid, wherein the control unit is designed in such a way that, in a first work cycle of successive work cycles, a first fluid circulation is formed in which spent liquid from the exchange vessel flows into the drain and is replaced by fresh liquid from the liquid source and, in a second work cycle of the successive work cycles, a second fluid circulation is formed in which fresh liquid from the exchange vessel flows into the treatment unit and is replaced by spent liquid from the treatment unit, and characterized by a pressure detector, connected to the control unit, for detecting the pressure in the exchange vessel during the first work cycle, the second work cycle and a third work cycle, and wherein the control unit is further designed to shut off the first and the second outflow line in the third work cycle, and the pressure in the exchange vessel is brought to a previously measured pressure, wherein the previously measured pressure corresponds to the higher of the pressures in the exchange vessel during the first work cycle and during the second work cycle, or to shut off the first and the second inlet line in the third work cycle, and the pressure in the exchange vessel is brought at the outlet side to a previously measured pressure, wherein the previously measured pressure corresponds to the lower of the pressures in the exchange vessel during the first work cycle and during the second work cycle.