A pump suitable for use in a wearable medical device, such as a patch pump, comprises an axially translatable chamber with an inlet and an outlet, a piston or a diaphragm rotatably received in the chamber, a first valve between the inlet and the chamber, a second valve between the outlet and the chamber, a cam affixed to the chamber, a follower affixed to the piston and in contact with the cam for axially translating the chamber, and a biasing means acting on the chamber for applying a force on the chamber in an axial direction of the chamber to maintain such contact.
