IP 313: Determination of air release value of lubricating and hydraulic oils

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  • Method adopted/last revised: 2023
  • Method reapproved: None
  • REF/ISBN: IP313-2935231
  • Status: Current
  • First printed in STM books: January 2001


This standard specifies a procedure for the determination of the measurement of the ability of turbine, gear and hydraulic oils to separate entrained air. It is applicable to both mineral and synthetic based products, but the current precision statement only applies to mineral oils.

NOTE 1 - Agitation of lubricating and hydraulic oils with air in equipment such as bearings, couplings, gears, pumps and lines, can 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 surface, a mixture of air and oil will circulate through the 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.

NOTE 2 - This standard measures the time for the entrained air content to fall to the relatively low value of 0,20 % (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, entrained air can cause sponginess and lack of sensitivity in the control of turbine and hydraulic systems. This standard may not be suitable for ranking oils in applications where residence times are short and gas contents are high.

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