Presently disclosed is a hydraulic pump device and its use thereof, especially in a fluid delivery system. In one embodiment, the fluid delivery system is an inexpensive, single-use device for slow dosing medicament applications. The fluid delivery system may employ a spring-compressed bellows crank or other combination of simple mechanisms operating according to the well-known peristaltic principle to force a volume of ultrapure bio-inert hydraulic fluid through an aperture, thereby expanding one chamber of a two chamber hydraulic cylinder. The second, fluid storage chamber, containing the medicament, is emptied through a conventional orifice in response to the expansion of the pump chamber. The medicament may thence flow through any suitable infusion set into a patient removeably attached thereto.