Abstract: A fluid oscillator is shown for producing pulsations in a flow of fluid. The oscillator has a housing which includes a fluid inlet channel for connection to a supply of fluid under pressure, a fluid outlet channel, and a valve chamber located between and communicating with said channels. A valve element is movably located in the valve chamber to alternatively block and unblock the outlet channel to produce the pulsating flow. The valve element moves to a blocking position by a reduction in fluid pressure at the valve element adjacent to the outlet channel. This reduction in pressure is partly caused by the fluid flowing past the valve element from the inlet channel to the outlet channel. The outlet channel is dimensioned so that the inertia of the fluid therein produces a further reduction in fluid pressure at the valve element adjacent to the outlet channel, which further reduction in pressure also holds the valve element firmly in the blocking position.