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Oil Aeration

To: List Land Speed <>
Subject: Oil Aeration
From: Bryan Savage <>
Date: Wed, 10 Sep 2003 10:52:37 -0700

One reason for a dry sump is removing the air from the oil. I don't know
( Dave ??) how much heat can be generated by air in engine oil but aeration
is a major cause of heat failure in hydraulic systems.

Bryan  (The information junkie)

The following is from:
Controlling Oil Aeration and Foam
Marianne Duncanson, Exxon Company USA

Dissolved air is not readily drawn out of solution. It becomes a problem 
when temperatures rise rapidly or pressures drop. Petroleum oils contain 
as much as 12 percent dissolved air. When a system starts up or when it 
overheats, this air changes from a dissolved phase into small bubbles. 
If the bubbles are less than 1 mm in diameter, they remain suspended in 
the liquid phase of the oil, particularly in high viscosity oils, 
causing air entrainment, which is characterized as a small amount of air 
in the form of extremely small bubbles dispersed throughout the bulk of 
the oil. Air entrainment is treated differently than foam, and is most 
often a completely separate problem. Some of the potential effects of 
air entrainment include:


      pump cavitation,


      oil oxidation,


      component wear due to reduced lubricant viscosity,


      micro-dieseling due to the ignition of the bubble sheath at the
      high temperatures generated by compressed air bubbles,

Base Oils Effects

In a system where foam is generated mechanically, switching to synthetic 
oil may help.


      Polyalphaolefin and hydrocracked oils, by virtue of their high
      surface tension, show relatively low foaming tendency compared to
      petroleum hydrocarbons.


      Unadditized organic esters are essentially nonfoaming, but are
      highly susceptible to contamination or to effects from additives.


      Phosphate esters show foam build-up at low temperatures, but
      above 122:F (50:C) they show very little foam tendency.

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