Required minimum (rated) viscosity v 1 as a function of bearing dimension and shaft speed. Oil overheating may be an additional concern.įigure 2. Oil rings, if used, would probably slow down and malfunction in such viscous oils. But that is unrealistically thick for most process pump bearings. The MRC Engineer's Handbook states, "In general, the oil viscosity should be about 100 Saybolt Universal Seconds (SUS) at the operating temperature." 1 If for some reason a bearing was operating at 210 degrees F, Figure 1 would call for a lubricant with an International Organization for Standardization (ISO) viscosity grade (VG) somewhere between 220 and 320. Whatever the user chooses, he or she must guard against using the thinnest oil found on the market to avoid the problem of inadequate oil film strength and thickness. They can use a jet of oil (oil spray) or convey the oil mixed with compressed air in the form of an oil fog-also called oil mist. Users can heat the oil or avoid oil rings and other risk-inducing lube application methods by using smarter means. Thick oils are more viscous and may not readily flow into the bearings. Figure 1 illustrates where these motor oils fit in comparison to the industrial oil designations used today. But thinner oils, perhaps SAE 10, can help prepare a vehicle for winter driving. Some will know from their experience with automobiles that thicker oils, such as Society of Automotive Engineers (SAE) 30, are more appropriate for warm summer months.
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