Piston diaphragm pumps are used worldwide to transport abrasive and/or aggressive slurries against high discharge pressures in the mining, mineral processing, and power industries. The limitation of the strain levels in the elastomer of the diaphragm is of utmost importance for eliminating fatigue failures of the diaphragm and thereby obtaining a high reliability of the piston diaphragm pump. The actual strain levels in the diaphragm are the result of a complex fluid structure interaction mechanism within the pump chamber. Understanding of this fluid structure interaction mechanism has improved in the last decades but is still limited. This paper first describes a detailed dimensional analysis of the fluid structure interaction mechanism and shows how it has been used to evaluate field experiences and how it is currently being used within robust design and selection rules for piston diaphragm pumps. Next, the paper describes the development of a numerical model for modelling the complex fluid structure interaction mechanism which enables the prediction of the resulting diaphragm deformation and strain levels. A novel combination of different immersed boundary approaches is used for modelling the fluid structure interaction phenomena. Furthermore an experimental setup is described whose results are used to validate the results of the numerical model. Some preliminary results of the numerical model and the experiments are shown.