A pump
system for an infusion
system includes a
linear drive (36, 36′) which minimizes the space occupied by the pump components in a portable housing (10, 10′). A motor (34) and a
motor drive shaft (42) are arranged in parallel with, and adjacent to a
syringe (14, 14′) and lead screw (94, 94′). A gear box (54) connects the
drive shaft and lead screw to transfer rotational movements between them. A
piston driving member, such as a drive nut (116) converts the rotational movement of the lead screw into
linear motion of a
syringe piston (24). A cap (190, 190′) couples the
syringe (14, 14′) to the housing and provides an outlet for the liquid to be dispensed. In one embodiment, the cap (190′) is configured to rotate relative to the housing in one direction only, during locking. Rotational movement is also used for locking the
piston (24) to the drive nut (116) against relative axial movement. In another embodiment, the cap (190′) carries a rotatable hub (330) which is connected at a first end (336) with an infusion line (191) and at a second end defines a needle (338) for piercing a closure (340) on the syringe.