Abstract

An outer wall member, such as the wall of a tube, connectable to or integral with the pipe, has an opening in communication with the exterior of the pipe. An inner member is fixedly positioned against the inside of the outer member for separating the opening from the fluid path through the pipe. The inner member has an inner surface defining at least a portion of an inner chamber in communication with the pipe fluid path. The inner and outer members define a labyrinth having an effective cross-sectional area, an inlet end for receiving pressurized fluid from the pipe, and an outlet end in communication with the pipe opening for emitting fluid. A plurality of channels couple intermediate portions of the labyrinth directly to the opening, thereby bypassing respective parts of the labyrinth. A resilient wall, functioning as a valve, forms a barrier between the channel and the inner chamber and is responsive to the pressure in the inner chamber for restricting the channel when the pressure exceeds a first predetermined pressure. This prevents the fluid from bypassing part of the labyrinth, increases the effective length of the labyrinth, and thereby reduces the flow that takes place at the higher pressure.