Medical apparatus comprising a medical machine and a manifold assembly, wherein the manifold assembly is mounted or mountable on the medical machine; the manifold assembly comprising: a casing comprising a rigid shell and at least one soft membrane, the rigid shell and soft membrane delimiting at least a first fluid passage for a fluid; the rigid shell comprising at least one port in fluid communication with said first fluid passage and with a second fluid passage for the fluid; the at least one port having a seat; said at least one soft membrane facing the seat of said at least one port; the seat is configured for accommodating, at least partially, a respective occlusion element of the medical machine; the medical machine comprising: at least one occlusion element; said occlusion element, when the manifold assembly is properly mounted on the medical machine, faces the seat with the soft membrane there between; the occlusion element comprising a plunger and an actuator; wherein the actuator is configured to move the plunger between a retracted position, in which the plunger is spaced from the soft membrane and the port is open, and a forward position, in which the plunger is at least in part accommodated in the seat and the soft membrane is trapped between said plunger and said seat to close the port; characterized in that the occlusion element comprises a membrane tensioner of mechanical type; wherein the membrane tensioner is configured to raise the soft membrane away from the seat when the plunger goes back to the retracted position and to counteract a possible negative pressure tending to keep the port closed. a casing comprising a rigid shell and at least one soft membrane, the rigid shell and soft membrane delimiting at least a first fluid passage for a fluid; the rigid shell comprising at least one port in fluid communication with said first fluid passage and with a second fluid passage for the fluid; the at least one port having a seat; said at least one soft membrane facing the seat of said at least one port; the seat is configured for accommodating, at least partially, a respective occlusion element of the medical machine; the medical machine comprising: at least one occlusion element; said occlusion element, when the manifold assembly is properly mounted on the medical machine, faces the seat with the soft membrane there between; the occlusion element comprising a plunger and an actuator; wherein the actuator is configured to move the plunger between a retracted position, in which the plunger is spaced from the soft membrane and the port is open, and a forward position, in which the plunger is at least in part accommodated in the seat and the soft membrane is trapped between said plunger and said seat to close the port; characterized in that the occlusion element comprises a membrane tensioner of mechanical type; wherein the membrane tensioner is configured to raise the soft membrane away from the seat when the plunger goes back to the retracted position and to counteract a possible negative pressure tending to keep the port closed. at least one occlusion element; said occlusion element, when the manifold assembly is properly mounted on the medical machine, faces the seat with the soft membrane there between; the occlusion element comprising a plunger and an actuator; wherein the actuator is configured to move the plunger between a retracted position, in which the plunger is spaced from the soft membrane and the port is open, and a forward position, in which the plunger is at least in part accommodated in the seat and the soft membrane is trapped between said plunger and said seat to close the port; characterized in that the occlusion element comprises a membrane tensioner of mechanical type; wherein the membrane tensioner is configured to raise the soft membrane away from the seat when the plunger goes back to the retracted position and to counteract a possible negative pressure tending to keep the port closed.