High pressure fluid systems, such as fuel injection systems for an engine or hydraulic controls, often experience high pressure fluctuations which can cause cavitation in the system components plus secondary fuel injection in the fuel systems. Apparatus (10) is provided for dampening the pressures in such systems, as well as filtering the fluid. The apparatus (10) has a filtering element (36) which does not substantially restrict fluid flow but is movable in response to pressure waves in the fluid which are directed onto the filtering element (36). The filtering element (36) thereby filters the fluid and tends to dampen the effects of the pressure waves, which create the pressure fluctuations, by resisting their movement through the fluid system.