Machinery's Handbook, 31st Edition
Lubricant Contamination 2519 A study conducted by the British Hydromechanics Research Association (BHRA) looked at the relationship between hydraulic fluid cleanliness and mean time between failure (MTBF) of over 100 hydraulic systems in a variety of industries over a three year period. The results are seen in Fig. 14 and show that systems that were successful in filter ing out and excluding contaminants over 5 microns in size lasted tens of thousand of hours longer between system breakdowns.
< 5 Microns
> 5 Microns
> 15 Microns
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Mean Time Between Failures (MTBF) 1000
Fig. 14. MTBF vs. Cleanliness Levels Solid particle ingression into a closed lubrication/hydraulic system can come from a va- riety of sources that include new oil, service and manufacturing debris, improper seals, vents/breathers, filter breakdown, and internal wear generation. For the most part, ingress prevention is all about filtration. Introducing filtered clean new oil into a system will sig nificantly retard the wear process and avoid clogging up breathers and in-line filter systems. Water Contamination .— Water contamination is the other major lubricant contaminant that will significantly degrade the oil’s life ( Fig. 15 ). Lubrication fluid typically saturates at 0.04% or 400 ppm, whereas hydraulic fluid (excluding water glycol fluids) saturates at an even lower 0.03% or 300 ppm. Typical water sources are found in the fluid storage areas when lubricants are stored outdoors and subjected to the elements, or stored in continu- ally changing temperatures causing condensation and rust that can be transferred into the equipment’s lubrication system.
0.0025% = 25 parts per million 0.50 % = 5000 ppm
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Percentage (%) of Water in Oil
Fig. 15. Effect of Water in Oil on Bearing Life
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