A pumping device is disclosed, as for use with an enteral feeding assembly. In one form the pumping device is a diaphragm pump including a first dome portion, a second dome portion, and a flexible membrane located between the first and second dome portions. A pressure differential is created between the two chambers thus created by membrane, so as to meter fluid (to be delivered) to a patient. The fluid to be delivered may be located in one of the chambers. A portable fluid pump is also provided including a syringe and spring pump drive mechanism mounted in a casing. The spring pump drive mechanism has two piston devices in fluid communication with each other. As one piston device moves in one direction within its associated driving barrel, it serves to drive the other piston device.