The paper presents the results of a study on the experimental determination and theoretical prediction of the source flow ripple generated by a fluid power piston pump. This work supports the development of quieter pumps with better fluidborne noise characteristics. As an effective experimental method, the “2 Pressures/2 Systems” method is introduced and used to determine the actual value of the source flow ripple and confirm the prediction results. A theoretical model is derived by the inclusion of the compressibility of the fluid, the fluid momentum in the cylinder chamber and relief grooves, and the pressure-dependent effective bulk modulus of the fluid containing air. The accuracy of the model is confirmed by the comparison of predicted and measured results. Finally, the effectiveness of the experimental method is presented.