An investigation has been made of the effectiveness of reinforced flexible hoses in decreasing pressure fluctuations in a hydraulic circuit. An understanding has been obtained of the properties and length of hose required to achieve a quieter system. The existing theory of longitudinal wave propagation in hoses has been extended by considering the effect of fluid viscosity and by making an accurate allowance for the inner lining. The theory has been checked by comparing the wave properties obtained from resonance tests with those calculated from the physical properties of hose and fluid by using the theory. A method of calculating pressure fluctuations in a complete hydraulic system consisting of one or more lengths of hose has been developed. In many cases, motion of the ends of hoses can be neglected which simplifies the calculations. The results for simple circuits have been compared with those obtained experimentally. A theoretical investigation has been made of the effects of the physical properties of a hose on the wave properties. It has been found helpful to split up wall stiffness into two components corresponding to actual or effective extension of the reinforcing cords and to changes in cord angle. There are two ways in which hoses can be used to reduce the pressure fluctuations in a system. A short tuned length of hose can be used to reduce pressure fluctuation at a particular frequency, or a longer length can be used for broadband attenuation. Both approaches have been investigated theoretically and experimentally, although only the latter is of general practical applicability. High attenuation is achieved with extensible cords and with high loss factors associated with wall deformation. For this reason nylon reinforced hoses are effective. The theory also enables the normal surface velocity of a hose, and hence the sound power radiated from it, to be calculated.
|Date of Award||1981|