Fluid transport systems are rarely at steady state. Transient phenomena, such as water hammer, can inflict severe physical damage. Repair costs can soar into the millions of dollars (Myers, 1997), and can reduce or even halt operation. Such high amplitude vibrations may be attenuated with particle dampers, which are beds of small particles placed in an attached enclosure or contained void. Vibration of the enclosure causes the particles to collide with each other and with the enclosure walls, resulting in energy dissipation through inelastic impacts and friction. Particle dampers have many advantages over conventional viscoelastic treatments including lower cost, increased robustness, greater effectiveness at high amplitudes and the ability to operate in extreme-temperature environments. Previous papers focus on exploration of sensitivity to design parameters, modeling techniques, and effective applications. However, there still remains much that is unknown about the phenomena and design of particle dampers. In this paper, experiments were performed to explore the effects of friction, excitation amplitude, and particle gap size. The formation of an oily residue on the colliding surfaces when certain materials were used increased friction and reduced damper effectiveness. This agrees with the theoretical prediction made by Mansour and Filho (1974). Damping was found to peak at an optimum gap size. Increasing the excitation amplitude resulted in higher damping and reduced sensitivity to the optimum gap size. Overall, the particle damper was deemed to be successful, increasing the loss factor of a clamped beam by over 10 times with a damper/structure mass ratio of only 0.016.