Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/704613
dryness target may be 250 parts per million or 0.025 percent for turbine oil. Air Air contamination has two general root causes. The first is related to machine or lubrication system operation where condi- tions produce high turbulence or low oil residence time in the sump. There may also be an air leak or very low pressure before the oil pump or in the return line. This will generate entrained air, which can lead to foaming. The second root cause involves the lubricant's condition or health. If a lubri- cant is contaminated, oxidized or has its anti-foam additive depleted, it will have more aeration problems. Some entrained air in the sump's return section may be normal due to the machine's operation. However, air should be considered a contaminant if it affects the lubricant health or machine operation. Air bubbles enhance the fluid's contact with oxygen, accelerating oxidation and acid formation. These bubbles may also produce microdieseling. Keep in mind that air is not a lubricant, so the oil film can fail in critical points. Cavitation may be the result of air bubbles or vapor imploding where the lubricant pressure increases in the circulating system. Air can also create a potential safety hazard. Excess foam may seep out of the system or cause spills that affect safety around the machine. For more on air contamination, see the article on defoamant additives in this issue. A simple field test to monitor lubricant health involves taking an oil sample from the sump and waiting 10 minutes for the foam to dissipate. If a significant amount of foam remains after 10 minutes, it may indi- cate a concern. Have your laboratory conduct a test to measure the foam tendency and foam stability or perform gas bubble separation. If a warning or alert level is not reported, the issue may be in the system operation. Oil analysis will be necessary to confirm whether the root cause of the air is in the oil. If it's not, you will need to inspect the entire system carefully to identify excessive churning conditions, verify the oil sump size or detect possible air leaks in the suction or return lines. Heat Heat may be generated by the machine's environment (ambient heat, steam, combustion, etc.), normal machine opera- tion or the fluid friction of oil in the lubrication system. Additional heat is produced when there is an abnormal condi- tion in the system, such as an incorrect