Hushing hydraulics

Researchers from the Georgia Institute of Technology put their energies into novel, compact devices for reducing fluid-borne noise.

Fluid-borne noise is a continual problem in fluid-power systems and is particularly difficult to treat. The speed of sound in hydraulic fluid is approximately 1400 m/s. The result is very long wavelengths at the frequencies of interest, which are related to the speed of the pumps used: a nine-piston, axial-piston pump typically has a piston-pass frequency of 270 Hz.

At that frequency, the wavelength of sound in the fluid would be over 5 m. Therefore, typical devices such as ¼- and ½-wavelength resonators would be far too large without some means of reducing the speed of sound. Such reduction is usually achieved by means of a pressurized bladder.