A pump-head , comprising: a pump housing comprising a first housing portion and a second housing portion that, when attached together, define a pump-cavity and a magnet-cavity in hydraulic communication with the pump-cavity, the pump-cavity containing at least one movable pumping element, the magnet-cavity containing a driven magnet that is coupled to the movable pumping element and magnetically coupled to a moving magnetic field produced outside the pump housing, wherein movement of the magnetic field causes corresponding movement of the driven magnet, which causes corresponding motion of the pumping element in the pump-cavity in a manner resulting in a pumped flow of liquid through the pump-cavity; the second housing portion comprising inlet and outlet ports in hydraulic communication with the pump-cavity, the second housing portion defining at least a portion of the magnet-cavity and at least a portion of the pump-cavity; the pump-head being characterised in that the first housing portion comprises a first circumferential threaded region and a wearable surface on which the pumping element is disposed, and in that the second housing portion comprises a second circumferential threaded region inside the second housing portion that is complementary to the first circumferential threaded region so that the first and second housing portions are attachable together by inserting and threading the first circumferential threaded region into the second housing portion such that the wearable surface and the pumping element are received in the second housing portion to form the pump housing, and the housing portions when unthreaded from each other allowing the at least one pumping element to be carried away with the detached first housing portion , thereby providing access to the at least one pumping element and the wearable surface without disconnecting the inlet and outlet ports of the second housing portion from a hydraulic circuit in the host system. a pump housing comprising a first housing portion and a second housing portion that, when attached together, define a pump-cavity and a magnet-cavity in hydraulic communication with the pump-cavity, the pump-cavity containing at least one movable pumping element, the magnet-cavity containing a driven magnet that is coupled to the movable pumping element and magnetically coupled to a moving magnetic field produced outside the pump housing, wherein movement of the magnetic field causes corresponding movement of the driven magnet, which causes corresponding motion of the pumping element in the pump-cavity in a manner resulting in a pumped flow of liquid through the pump-cavity; the second housing portion comprising inlet and outlet ports in hydraulic communication with the pump-cavity, the second housing portion defining at least a portion of the magnet-cavity and at least a portion of the pump-cavity; the pump-head being characterised in that the first housing portion comprises a first circumferential threaded region and a wearable surface on which the pumping element is disposed, and in that the second housing portion comprises a second circumferential threaded region inside the second housing portion that is complementary to the first circumferential threaded region so that the first and second housing portions are attachable together by inserting and threading the first circumferential threaded region into the second housing portion such that the wearable surface and the pumping element are received in the second housing portion to form the pump housing, and the housing portions when unthreaded from each other allowing the at least one pumping element to be carried away with the detached first housing portion , thereby providing access to the at least one pumping element and the wearable surface without disconnecting the inlet and outlet ports of the second housing portion from a hydraulic circuit in the host system. <EOS>