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Title: Oil stiction in automatic compressor valves
Author: Pringle, Samuel
ISNI:       0000 0001 3501 8241
Awarding Body: University of Strathclyde,
Current Institution: University of Strathclyde
Date of Award: 1976
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This thesis describes experimental and theoretical investigations into oil stiction effects in automatic compressor valves. The experimental programme involved the testing of disc valves in a compressor in which the working fluid could be varied and the oil circulation controlled. The main purpose of the experiment was to measure, in as direct a manner as possible, the time lag in valve opening due to the presence of oil between the valve disc and its seat. The design of the apparatus also allowed the pressure difference across the valve, required to open it, to be measured. These tests were carried out under various conditions of back pressure and rate of change of pressure. The experimental progranme also involved the measurement of the stiction force in a test rig in which the parameters of seat geometry, oil viscosity, and rate of application of lift on the valve disc could be controlled. The stages involved in the rupture of the oil film are described and coefficients obtained from the analysis of these test results are utilised in conputer programs which simulate the stiction process in a working compressor. The theoretical model, for the simulation of the phenomena during the initial opening phase of the valve, is based on the Navier-Stokes Equations lasing thin film approximations. The theoretical model is programmed for use in a digital computer. Subroutines in the programs take account of surface tension and cavitation in the oil film. The model is not completely analytical. As stated above, it utilises a number of experimentally determined coefficients, modified to suit conditions in a working compressor. Both the effect of rate of change of pressure across the valve and flexure of the valve are shown by the mathematical model to be significant. Trends indicated by variation of these parameters and others, such as seat geometry and oil viscosity, are mirrored by experimental results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral