Sound damping for air supply duct for pneumatic brake servo

摘要

The air speed through the duct is sub-sonic. Upstream of the sound source (5) and baffle (3) restricts the ir flow through a number of shaped jets (4) with the air speed inside the jets super sonic with the shaping of the jets designed to minimise sound generation. A plastic moulded baffle with Laval jets provides a simple fitting into the non porous gas duct. The jet profile tapers from an inlet aperture (7) to a minimum aperture (8) from where a second slope ducts the gas into a diverging pattern to aide outlet aperture (9). The inlet aperture is 1.01 to 2.5 times the area of the minimum aperture while th outlet aperture is 1.05 to 4 times the area of the minimum aperture. The jet profile is progressive and the jet length is 4 to 12 times the diameter of the minimum aperture.