A pump apparatus that exerts a constant force on a bag of fluid to provide a uniform flow rate compared to elastomeric pumps. The apparatus comprises a first and a second block member positioned over a plate, which are moveable to define an opening to receive a wedge member attached on the plate. The block members are coupled by a resilient means that is extendable when the wedge member is urged into the opening. The extended resilient means is retractable such that the plate exerts a constant force on the bag to expel fluid in a uniform flow rate.
