The effects of pump fluctuations on cyclone performance were investigated. Flow patterns of three commercially available pumps, the MSA model-G, the Bendix Micronair II, and the DuPont P-2500, were analyzed at the pump and cyclone inlets of a 10 millimeter nylon cyclone. Flow rate was 2.0 liters per minute (l/min). Amplitudes corresponding to the various harmonics of each pump flow were then computed using a Fourier transform technique. Amplification exhibited a resonant structure characterized by peaks near odd multiples of the frequency of a sound wave with wavelength equal to four times the length of the air column. The effect of flow rate on frequency and amplitude of primary fluctuations of the pumps was evaluated at flow rates of 2.0 and 1.2l/min. Increasing the flow rate decreased the amplitude and frequency of the fluctuations of the MSA and Bendix pumps. Fluctuation frequency, but not amplitude, of the DuPont pump decreased with increasing air flow rate. The effects of pump pulsations on cyclone penetration were evaluated by measuring the aerodynamic diameters of particles penetrating the cyclone at sinusoidal pulsation frequencies of 0, 34, and 64 hertz at flow rates of 1.5 to 2.51/min. Experimental and theoretical penetration curves were constructed. Pulsations of increasing frequency shifted the particle distributions toward smaller aerodynamic diameters. The larger particles penetrated less as the pulsation frequency increased. The authors conclude that the fluctuation induced penetration shifts include a significant frequency dependent contribution that increases rapidly with aerodynamic diameter.