A medical apparatus for the preparation of medical fluid, comprising: a support structure; a movable member, movably mounted to the support structure and carrying a first port; a first fluid line carried by the support structure and configured to be put into fluid communication with a source of fluid, the first fluid line being in fluid communication with the first port; a second fluid line carried by the support structure and being in fluid communication with a second port; biasing means; and locking means; wherein the first port is configured to receive a first connection port of a container of at least one substance to be added to a fluid coming from the source of fluid; the movable member is mounted to the support structure for movement between at least a retracted configuration, in which the first port and the second port are coupled to each other, and an unretracted configuration, in which the first port and the second port are spaced apart from each other; the locking means are configured to releasably hold the movable member in its retracted configuration; and the biasing means are configured to operate in at least one of a repulsion mode and an attraction mode, wherein - in their repulsion mode, the biasing means are configured to exert on the movable member, at least when the locking means release the movable member from its retracted configuration, a biasing force directing the movable member away from its retracted configuration, and - in their attraction mode, the biasing means are configured to exert on the movable member, at least when the movable member is in its unretracted configuration, the biasing force directing the movable member towards its retracted configuration, characterized in that the biasing means comprise a first magnetic element and a second magnetic element, the first and second magnetic elements being configured to exert the biasing force. a support structure; a movable member, movably mounted to the support structure and carrying a first port; a first fluid line carried by the support structure and configured to be put into fluid communication with a source of fluid, the first fluid line being in fluid communication with the first port; a second fluid line carried by the support structure and being in fluid communication with a second port; biasing means; and locking means; wherein the first port is configured to receive a first connection port of a container of at least one substance to be added to a fluid coming from the source of fluid; the movable member is mounted to the support structure for movement between at least a retracted configuration, in which the first port and the second port are coupled to each other, and an unretracted configuration, in which the first port and the second port are spaced apart from each other; the locking means are configured to releasably hold the movable member in its retracted configuration; and the biasing means are configured to operate in at least one of a repulsion mode and an attraction mode, wherein - in their repulsion mode, the biasing means are configured to exert on the movable member, at least when the locking means release the movable member from its retracted configuration, a biasing force directing the movable member away from its retracted configuration, and - in their attraction mode, the biasing means are configured to exert on the movable member, at least when the movable member is in its unretracted configuration, the biasing force directing the movable member towards its retracted configuration, characterized in that - in their repulsion mode, the biasing means are configured to exert on the movable member, at least when the locking means release the movable member from its retracted configuration, a biasing force directing the movable member away from its retracted configuration, and - in their attraction mode, the biasing means are configured to exert on the movable member, at least when the movable member is in its unretracted configuration, the biasing force directing the movable member towards its retracted configuration, characterized in that the biasing means comprise a first magnetic element and a second magnetic element, the first and second magnetic elements being configured to exert the biasing force.