Mandrels and elastomeric pumps for infusion assemblies are provided. For example, a mandrel may comprise a body extending over a length from a first end to an opposing second end； an outer diameter； a bore extending within the body； an inlet port defined near the first end； and a fill port defined between the first and second ends. The inlet and fill ports are in fluid communication with the bore. The outer diameter of the mandrel at a midpoint of the length is different than the outer diameter at each of the first end and the second end. In some embodiments, the outer diameter of the mandrel gradually transitions from a first outer diameter at the first end to a second outer diameter at the second end. An elastomeric pump may include an exemplary mandrel and an inflatable elastomeric bladder disposed on the mandrel.
