A dialysis system comprising: a pumping cassette having a generally planar body and a first flexible membrane on a side of the cassette overlying a pumping chamber on the cassette; and a cycler having a control surface including a second flexible membrane arranged to contact and mate with the first flexible membrane of the pumping cassette, the cycler being arranged to move one or more portions of the second flexible membrane to move at least a portion of the first flexible membrane overlying a pumping chamber on the cassette to cause fluid flow in the pumping chamber, the cycler further including at least one port at the control surface arranged to remove fluid in a space between the first and second flexible membranes to draw the first and second flexible membranes toward each other and to introduce fluid into the space to move the first and second flexible membranes away from each other, wherein: the system comprises a controller; the cycler comprises a source of positive pressure and a source of negative pressure; the cycler includes a valved manifold to control flow of negative and positive pressure to the at least one port, the manifold comprising a fluid trap, wherein the fluid trap includes a sensor to detect liquid drawn from the at least one port to the fluid trap and a pressure sensor to detect pressure in the fluid trap; the cycler includes a pressure delivery block that backs the control surface and includes at least one control chamber or depression (171A, 171B) in association with corresponding control regions (1481, 1482) of the control surface, each control chamber or depression being arranged to move the corresponding control region based on a fluid pressure in the control region or depression; the at least one port is able to be supplied with positive pressure by temporarily connecting the at lest one port to the positive pressure source, the at least one port is normally connected to the negative pressure source via the fluid trap in the manifold during therapy, the controller is configured to control the valved manifold to selectively provide negative pressure to the at least one port during therapy and provide positive pressure to the at least one port to pressurize the fluid in the fluid trap and the at least one port so that the pressurized fluid will flow through the at least one port and between the first membrane and the control surface, breaking any vacuum bond between the first membrane and the control surface. a pumping cassette having a generally planar body and a first flexible membrane on a side of the cassette overlying a pumping chamber on the cassette; and a cycler having a control surface including a second flexible membrane arranged to contact and mate with the first flexible membrane of the pumping cassette, the cycler being arranged to move one or more portions of the second flexible membrane to move at least a portion of the first flexible membrane overlying a pumping chamber on the cassette to cause fluid flow in the pumping chamber, the cycler further including at least one port at the control surface arranged to remove fluid in a space between the first and second flexible membranes to draw the first and second flexible membranes toward each other and to introduce fluid into the space to move the first and second flexible membranes away from each other, wherein: the system comprises a controller; the cycler comprises a source of positive pressure and a source of negative pressure; the cycler includes a valved manifold to control flow of negative and positive pressure to the at least one port, the manifold comprising a fluid trap, wherein the fluid trap includes a sensor to detect liquid drawn from the at least one port to the fluid trap and a pressure sensor to detect pressure in the fluid trap; the cycler includes a pressure delivery block that backs the control surface and includes at least one control chamber or depression (171A, 171B) in association with corresponding control regions (1481, 1482) of the control surface, each control chamber or depression being arranged to move the corresponding control region based on a fluid pressure in the control region or depression; the at least one port is able to be supplied with positive pressure by temporarily connecting the at lest one port to the positive pressure source, the at least one port is normally connected to the negative pressure source via the fluid trap in the manifold during therapy, the controller is configured to control the valved manifold to selectively provide negative pressure to the at least one port during therapy and provide positive pressure to the at least one port to pressurize the fluid in the fluid trap and the at least one port so that the pressurized fluid will flow through the at least one port and between the first membrane and the control surface, breaking any vacuum bond between the first membrane and the control surface.