A new type of pneumatic oscillator is presented which produces triangular waveforms of pressure versus time. The device can be used for both high power and low power applications. It utilizes a freely floating disk which translates back and forth a short distance inside a housing between two dynamically unstable flapper nozzle valves. A theoretical analysis of the performance and stability of the device is given. A simplified analysis and design procedure which accounts for load flow is shown. Several prototype units were successfully operated and the experimental results obtained with them are described and compared with the predicted results.