A pump, comprising: a pump housing comprising pressure-boundary walls defining a pump cavity, the pump housing having first and second housing portions conjoined with each other by a dynamic seal (618; 819) allowing movement of at least one housing portion relative to the other housing portion in response to a pressure condition in the pump cavity by automatically changing a volume of the pump cavity at least while the pump cavity is primed with fluid, the housing further defining at least one inlet (604; 817) and at least one outlet (606; 818); a bias, situated relative to the first and second portions of the pump housing and providing a selected counter-force to the movement of the housing portion(s); a movable pumping member situated in the pump cavity and, when driven to move, urging flow of the fluid from the inlet (604; 817) through the pump cavity to the outlet (606; 818); and a mover coupled to the pumping member so as to drive pumping motions of the pumping member, wherein the pump cavity is symmetrical about an axis, the dynamic seal (618; 819) is configured to allow movement of at least one portion of the housing along the axis to relieve the pressure condition, the first portion of the housing comprises a respective cylindrical portion, and the second portion of the housing comprises a respective cylindrical portion that is slip-fit into the cylindrical portion of the first portion, the dynamic seal (618; 819) comprises at least one ring seal situated between the respective cylindrical portions, the respective cylindrical portion of the first portion of the housing comprises a magnet cup having an interior housing, a driven magnet, and that is a respective portion of the pump cavity; and the dynamic seal (618; 819) is between the magnet cup and the cylindrical portion of the second portion of the housing. a pump housing comprising pressure-boundary walls defining a pump cavity, the pump housing having first and second housing portions conjoined with each other by a dynamic seal (618; 819) allowing movement of at least one housing portion relative to the other housing portion in response to a pressure condition in the pump cavity by automatically changing a volume of the pump cavity at least while the pump cavity is primed with fluid, the housing further defining at least one inlet (604; 817) and at least one outlet (606; 818); a bias, situated relative to the first and second portions of the pump housing and providing a selected counter-force to the movement of the housing portion(s); a movable pumping member situated in the pump cavity and, when driven to move, urging flow of the fluid from the inlet (604; 817) through the pump cavity to the outlet (606; 818); and a mover coupled to the pumping member so as to drive pumping motions of the pumping member, wherein the pump cavity is symmetrical about an axis, the dynamic seal (618; 819) is configured to allow movement of at least one portion of the housing along the axis to relieve the pressure condition, the first portion of the housing comprises a respective cylindrical portion, and the second portion of the housing comprises a respective cylindrical portion that is slip-fit into the cylindrical portion of the first portion, the dynamic seal (618; 819) comprises at least one ring seal situated between the respective cylindrical portions, the respective cylindrical portion of the first portion of the housing comprises a magnet cup having an interior housing, a driven magnet, and that is a respective portion of the pump cavity; and the dynamic seal (618; 819) is between the magnet cup and the cylindrical portion of the second portion of the housing.