(Equivalent Test Methods: IP 313, ISO 9120, DIN 51381, and AFNOR E48-614)
EXPLANATION
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.
This test measures the time for the entrained air content to fall to the relatively low value of 0.2 % volume 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. The significance of this test has not been fully established. However, 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. Currently the applicability of this test method appears to be directed towards turbines manufactured outside the United States. It may not be suitable for ranking oils in applications where residence times are short and gas contents are high.
TEST SUMMARY
Compressed gas is blown through the test oil which has been heated to a temperature of 25, 50, or 75° C. After the gas flow is stopped, the time required for the gas entrained in the oil to reduce in volume to 0.2 % is recorded as the gas bubble separation time. Gas bubble separation time is defined as the number of minutes needed for gas entrained in the oil to reduce in volume to 0.2 % under the conditions of this test and at the specified temperature.
TEST PRECISION
