In this research the application of the power spectral density (PSD) in an external gear hydraulic pump for fault diagnosis was investigated. For this purpose, the spectrum of pump vibration signals in the both good and journal-bearing with inner face wear (BIFW) conditions in the three working speeds of engine (1000, 1500, and 2000 rpm) were obtained. Results show that fault diagnosis of hydraulic pumps is difficult using spectrum of vibration signals alone. But with calculate the area under PSD curves, fault detection is easily obtainable.
