This International Standard specifies a method for the estimation of the ability of a petroleum-type steam turbine oil to be separated from entrained air. NOTES 1 The impinger method described in this International Standard is used for determining the air-release ability of the oils tested. Air bubbles dispersed in the oil influence the compressibility and can cause malfunctions. This method may not be suitable for ranking oils in applications where residence times are short and gas contents high.




2 Agitation of lubricating oil with air in equipment such as bearings, couplings, gears, pumps and oil return lines, may produce a dispersion of finely divided air bubbles in the oil. If the residence time in the reservoir is too short to allow the air bubbles to rise to the oil surface, a mixture of air and oil will circulate through the lubricating oil system. This may result in an inability to maintain oil pressure (particularly with centrifugal pumps), incomplete oil films in bearings and gears, and poor hydraulic system performance or failure.




3 This test measures the time for the entrained air content to fall to the relatively low value of 0,2 % (V/V) under a standardized set of test conditions, and hence permits the comparison of the ability of oils to separate entrained air under conditions where a separation time is available. Although the significance of the test results is not fully established, sponginess and lack of sensitivity of the control systems of some turbines may be related to the air release properties of the oil. System design and system pressure are other variables.




4 For the purposes of this International Standard, the expression “%(V/V)” is used to represent the volume fraction of a material