Modern Applied Science June, 2009 59 Vibration-Based Fault Diagnosis of Hydraulic Pump of Tractor Steering System by Using Energy Technique Kaveh Mollazade (Corresponding author) Department of Agricultural Machinery Engineering, Faculty of Biosystems Engineering University of Tehran, P.O. Box 4111, Karaj 31587-77871, Iran Tel: 98-918-972-0639 E-mail: kaveh.mollazade@gmail.com, mollazade@ut.ac.ir Hojat Ahmadi Department of Agricultural Machinery Engineering, Faculty of Biosystems Engineering University of Tehran, P.O. Box 4111, Karaj 31587-77871, Iran Mahmoud Omid Department of Agricultural Machinery Engineering, Faculty of Biosystems Engineering University of Tehran, P.O. Box 4111, Karaj 31587-77871, Iran Reza Alimardani Department of Agricultural Machinery Engineering, Faculty of Biosystems Engineering University of Tehran, P.O. Box 4111, Karaj 31587-77871, Iran Abstract This paper focuses on a problem of vibration-based condition monitoring and fault diagnosis of pumps used in the tractor steering system. The vibration signal from a piezoelectric transducer was captured for the following conditions: normal pump, journal-bearing with inner face wear, gear with tooth face wear, and journal-bearing with inner face wear plus gear with tooth face wear for three working levels of pump speed (1000, 1500, and 2000 rpm). Then Power Spectral Density (PSD) of vibration spectra was then calculated. Results showed that peak value of PSD was occurred in the frequency range between 70-120 Hz for all conditions. Comparison of numerical data produced by calculation the area under PSD v. frequency diagram showed that energy technique is an effective method for fault diagnosis of external gear hydraulic pumps. Keywords: Power spectral density, Vibration signal, External gear pump, Fault diagnosis 1. Introduction Nowadays, hydraulic pumps are more widely used in the power transmission system of automobiles and tractors as a main part of their hydraulic system. Steering system of modern tractors is equipped with both mechanical and hydraulic systems. Use of hydraulic power in the steering system can provide a facilitated steering for driver of tractor in the hard condition of farm lands. Hydraulic pumps are available in several types and are consisting of rotating and reciprocating parts (Srivastava, 2006). The detection and understanding of condition degradation in the pump is important for pump design and maintenance. For pump condition monitoring, the processing and analysis of the measured signal is the common way of extracting reliable feature representative of the pump condition (Mollazade et al., 2008). Condition monitoring provides information on the health and maintenance requirement of machinery and is used in a wide range of industrial applications. Parameters such as vibration, temperature, lubricant quality and power