Performance Prediction of an Axial Piston Pump With Increasing Severity of Leakage Fault in Single and Multiple Cylinders

As axial piston pumps (APP) become increasingly compact to meet the size, weight, and performance demands (high pressure ratings), they are prone to wear, and hence the leakage between the sliding parts, which run under tight tolerances. This leakage fault can degrade the pump's performance and limit its predictability and reliability. In this study, a simulation and mathematical model-based approach are presented to simulate the effect of increasing severity of leakage fault (increasing annular gap) in both single, and multiple cylinders simultaneously, on the pump performance. The Leakage is modeled as laminar flow past the uniform annular gap between the piston and cylinder. With a single faulty cylinder, as the wear (annular gap) increases the time-mean outlet flow and pressure of the pump remain constant until a critical threshold, and then reduce rapidly, leading to deterioration in the pump's volumetric efficiency. With increase in faulty cylinders this critical threshold shifts to lower magnitudes, and in the limit of more than four faulty cylinders this threshold saturates to a constant magnitude. The dynamic signal's data show that the increasing severity of leakage and increasing number of faulty cylinders modulate both the time signature and the amplitude fluctuations of the outlet pressure waveform due to the reduced flow in the discharge cycle. Further, FFT analysis of these dynamic signals, and the time-mean value of pressure and flow rate leakage fault diagnosis is presented to classify the pump's condition as either healthy or moderately faulty or severely faulty.