The fluid borne noise characteristics of hydraulic components and their measurement.
This thesis is concerned with the development of test techniques for
evaluating the fluid borne noise characteristics of components found
in hydraulic systems; in particular the source impedance and source
flow of positive displacement pumps.
A number of proposals for measuring the fluid borne noise generation
potential of positive displacement pumps are critically reviewed.
Particular attention is paid to the high impedance pipe technique
which is to be proposed as a British Standard.
An apparently simple method of obtaining the source characteristics
of a pump using only two transducers is shown to have serious drawbacks
due to magnified errors at resonant line length conditions.
A computer based scheme, capable of predicting the source and
termination characteristics of a pump-pipeline-termination system is
developed. The scheme is iterative and based on fitting the surface
of least squares error through a series of experimental pressure
readings. The technique requires the pressure ripple to be measured
at a number of points along a pipeline and for a series of different
pipe lengths. A special rig has been designed and built to
facilitate the data acquisition.
Using the technique, the source flow and source impedance characteristics
of a number of axial piston and gear pumps are examined.
The results obtained show very good agreement with theory and clearly
demonstrate the effects of pressure and speed on the source flow.
The impedance of several terminations are also predicted. For an
expansion chamber the predicted entry impedance is shown to deviate
from simple theory and this is attributed to vibration of the chamber.
The impedances of restrictor and relief valves are shown to be quite
complicated freqeuncy dependent functions and it is demonstrated that
significant errors in pressure ripple prediction may result from the
use of over-simplified models.