TECHNICAL ARTICLE Pressure Determination Approach in Specific Pressure Regions and FEM-Based Stress Analysis of the Housing of an External Gear Pump R. Cinar 1 , M. Ucar 2 , H.K. Celik 3 , M.Z. Firat 4 , and A.E.W. Rennie 5 1 Department of Mechanical Education, Institute of Natural and Applied Sciences, Kocaeli University, Kocaeli, Turkey 2 Department of Automotive Engineering, Technology Faculty, Kocaeli University, Kocaeli, Turkey 3 Department of Agricultural Machinery, Faculty of Agriculture, Akdeniz University, Antalya, Turkey 4 Department of Animal Science, Faculty of Agriculture, Akdeniz University, Antalya, Turkey 5 Lancaster Product Development Unit, Engineering Department, Lancaster University, Lancaster, UK Keywords External Gear Pump, Hydraulic Pressure Measurements, Stress Analysis Correspondence H.K. Celik, Department of Agricultural Machinery, Faculty of Agriculture, Akdeniz University, Antalya Turkey Email: hkcelik@akdeniz.edu.tr Received: September 3, 2013; accepted: February 13, 2014 doi:10.1111/ext.12086 Abstract In this study, an application algorithm has been introduced to explore structural optimisation for gear pump housing. In the study, experimental and theoretical (analytical and numerical) methods are utilised. A commercial external spur gear pump which has 17.1 L min −1 volumetric flow rate with maximum pressure capacity of 250 bar has been considered for an application case study. In the experimental section of the study, four pressure sensors (emitters) were placed with angle intervals of 45 ◦ , 90 ◦ , 135 ◦ , and 180 ◦ on the pump’s housing to measure operating pressure values at specific pressure regions of the housing from inlet to outlet. According to experimental results of the pressure measurements, a response surface analysis (RSA) was carried out and then an estimation model (empirical equation), which could be used to calculate pressure values at any specific region of the housing, was obtained. According to the RSA results gained, it appears that the estimation model has 99.9% R 2 value which can be used for adequately predicting accurate pressures at any region of the housing. Subsequently, this estimation model has been adapted for commercial finite element method (FEM)-based engineering software and from which stress distributions on the housing were simulated three dimensionally. FEM-based simulation outputs showed that there were no failure signatures on the pump housing. As the main conclusion of the study, it is seen that an estimation model gives an adequate approach to predict pressure values at any specific pressure region of the pump housing and, especially, stress distribution results has highlighted that a structural optimisation study may be suitable for the pump housing. Introduction One of the positive displacement types of hydraulic pump is the external gear pump. The gear pump is among the oldest and the most commonly used pumps in the wide range of application areas from agricultural machinery to heavy industrial machinery systems. 1 It has become the main choice for applicants due to long life, minimum maintenance, high reliability, capability in high-pressure operations, etc. Basically, an external gear pump converts mechanical power into hydraulic fluid power with high pressures. This converting operation is described as follows. 2 The shaft of one of the gears is driven by a motor. This gear is known as the driving gear. It engages around the other, known as the driven gear. When the teeth of the two gears start disengaging (near the centre of the pump), the consequent low pressure sucks in the fluid. Upon further rotation, the fluid is trapped in between the void formed by this cavity and the housing. The fluid is then carried around towards Experimental Techniques (2014)  2014, Society for Experimental Mechanics 1