Cassette for pumping a treatment solution through a dialyzer

A dialysis machine comprising:

• a cassette for pumping a treatment solution through a dialyzer in a dialysis system, said cassette including
• a body,
• a hydraulic manifold which is defined inside the body and configured for fluid communication with a first hydraulic connector on the body, the first hydraulic connector being arranged for connecting the dialyzer to the cassette,
• a pneumatic manifold which is defined inside the body and configured for fluid communication with a first pneumatic connector on the body, the first pneumatic connector being arranged for connecting the cassette to a pneumatic pressure source,
• a set of solution pumps integrated in the cassette, each solution pump of the set of solution pumps including a pump cavity which is defined inside the body for fluid communication with the hydraulic and pneumatic manifolds, and
• a valve arrangement which is operable to selectively communicate the pump cavity with the hydraulic and pneumatic manifolds so as to, during the operation of the respective solution pump, reciprocate an interface in the pump cavity and thereby displace the treatment solution through the hydraulic manifold,
• wherein each of the pump cavities defines, during operation of the respective solution pump, said interface as a direct gas-to-liquid interface in the pump cavity between a gaseous substance admitted via the pneumatic manifold and the treatment solution admitted via the hydraulic manifold;
• and
• a controller configured to control the operation of the valve arrangement.

A method of operating a cassette for pumping a treatment solution through a dialyzer in which the cassette includes (i) a body, (ii) a hydraulic manifold which is defined inside the body and configured for fluid communication with a first hydraulic connector on the body, the first hydraulic connector being arranged for connecting the dialyzer to the cassette, (iii) a pneumatic manifold which is defined inside the body and configured for fluid communication with a first pneumatic connector on the body, the first pneumatic connector arranged for connecting the cassette to a pneumatic pressure source, (iv) a set of solution pumps integrated in the cassette, each solution pump of the set of solution pumps including a pump cavity which is defined inside the body for fluid communication with the hydraulic and pneumatic manifolds, and (v) a valve arrangement which is operable to selectively communicate the pump cavity with the hydraulic and pneumatic manifolds so as to, during operation of the respective solution pump, reciprocate an interface in the pump cavity and thereby displace the treatment solution through the hydraulic manifold, (vi) an upstream subsystem for providing the treatment solution to the dialyzer via the first hydraulic connector, and a downstream subsystem for pumping the treatment solution from the dialyzer via a second hydraulic connector on the body,

• wherein each of the pump cavities defines, during operation of the respective solution pump, said interface as a direct gas-to-liquid interface in the pump cavity between a gaseous substance admitted via the pneumatic manifold and the treatment solution admitted via the hydraulic manifold, and
• wherein the set of solution pumps includes an upstream solution pump in the upstream subsystem and a downstream solution pump in the downstream subsystem,
• (vii) a calibration subsystem for relatively calibrating the upstream solution pump and the downstream solution pump, wherein the calibration subsystem includes a calibration cavity which is defined inside the body and connected for fluid communication with a bypass line that extends between the upstream and downstream solution pumps, and
• wherein level detectors are associated with the upstream and downstream solution pumps to indicate levels of the treatment solution in the respective pump cavity, wherein the cassette is operable to reciprocate the direct gas-to-liquid interface between an upper level and a lower level in the respective pump cavity so as to pump the treatment solution between the upstream and downstream solution pumps through the bypass line, and wherein the valve arrangement is operable to selectively control the fluid communication between the bypass line and the calibration cavity, said method comprising:
• (a) operating the valve arrangement during a calibration phase to cause:
• (a1) one of the upstream and downstream solution pumps to perform an emptying stroke that moves the direct gas-to-liquid interface from an upper reference level to a lower reference level so as to push the treatment solution into the bypass line, and (a2) cause the other of the upstream and downstream solution pumps to perform a filling stroke that moves the direct gas-to-liquid interface from a lower reference level to an upper reference level so as to draw the treatment solution from the bypass line, and selectively establish fluid communication between the bypass line and the calibration cavity during the emptying and filling strokes so as to transfer a known or measurable calibration volume between the calibration cavity and the pump cavity of the upstream solution pump or the downstream solution pump, wherein one of the level detectors is operable to measure a level change corresponding to the calibration volume in said pump cavity of the upstream solution pump or the downstream solution pump;
• (b) determining, during the calibration phase, a balancing level (h0) in said pump cavity of the upstream solution pump or the downstream solution pump, such that the filling and emptying strokes have equal volumes when the balancing level (h0) replaces the lower or upper reference level in said pump cavity;
• and
• (c) determining an adjusted stroke length for the direct gas-to-liquid interface in said pump cavity of the upstream solution pump or the downstream solution pump as a function of the level change (Δh), the balancing level (h0), and the calibration volume (VCAL), so as to achieve a given volumetric difference (VUF) between the upstream and downstream solution pumps.