This paper discusses the relationship between acoustic emission (AE) and different types of defect in pneumatic cylinders, shedding light on a new approach to determining these types of defect and distinguishing between them through acoustic emission. Difficulties facing the defect detection process are related to the types of defect that occur and the methods available for detection. A detection coefficient has been assigned to each cylinder by applying different methods of non-destructive testing (NDT) where a set of cylinders, which have defects that are difficult to detect, were determined. Two of the defects in those cylinders are made artificially and it is difficult to discover the differences between undamaged and damaged cylinders in this set using methods currently available. Therefore, the necessary parameters for comparison have been selected after analysing the signals that were obtained from the tests. The average energy of acoustic emission signal root mean square (RMS) provides a clear picture of the different responses between damaged and undamaged pneumatic cylinders.