Hydraulic piston pump failures may be related to either hardware or fluid problems. In some cases, apparent hardware failures have been traced to various fluid problems. In this paper, selected examples of pump failures will be provided to illustrate some common modes of axial piston pump failures. In most cases, these will represent actual failures including: misalignment, insufficient fluid lubrication, particle contamination, brinelling, corrosion, and cavitation. Various examples of these and other pump failure modes are provided.