Lubrication Tips for Reliability Professionals

July 17, 2001 Subscribers: 7,796

Q & A

"I operate 2 small generating stations. There is one 5hp compressor at each station. They are used to maintain air pressure to an obermeyer system (inflatable bladders which support flood gates.) One bladder has a serious leak causing one compressor to run almost constantly. This unit is never off long enough to cool off. I estimate outside volume tank temperature to be 103°F. The OEM specifications call for a specific brand name 30W nondetergent compressor oil. My question is: Will using "brand X" 30W oil lead to catastrophic failure or premature degradation of components?"

Compressors require highly engineered lubrication products to operate safely and efficiently.

Good compressor lubrication requires a lubricant with proper viscosity at operating temperature, high affinity for the metal surface and very low free carbon content. If your selected 30W is designed for lubrication of single and double cycle compressor crankcase and cylinder lubrication then you are likely using a product that can support the equipment effectively.

If your 30W is designed for other purposes then you may wish to look very closely at the manufacturer specifications to determine if you have enough of the right components in the lubricant to do the job.

Compressor oils are highly specialized. The specified oil is intended for use in high temperature single and double stage crank and cylinder service. I do not mean to promote the specific product but I certainly would like to validate the use of a product designed specifically for compressor service.

There are many factors that may lead to catastrophic failure. I cannot say that any single one, short of not lubricating the equipment or neglecting the normal lubrication maintenance practices, will cause a catastrophic failure. Using the wrong oil may contribute to rapid failure.

If it were my equipment I would want to make certain that I was using a 30W specifically designed for compressor service. If I was not, I would not sleep well at night.

Today's Tip

• The only way that the flash point of an oil can decrease over time is by the addition of a contaminant with a lower flash point. In a diesel engine, this is almost certainly a fuel leak. Since diesel fuel is chemically very similar to engine oil, it cannot be removed by filtration or any other means. The long term solution to this problem is to find the source of the fuel leak and correct it. Then you must change the oil since a fuel leak will decrease the viscosity and hence the oils ability to form an adequate lube oil film.

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Book Bits

Fatigue is a progressive process, beginning with microscopic cracks at regions of stress concentration on the contact surface or in the highly stressed subsurface region. Repeated stresses from the rolling contacts cause cracks to form and grow until several cracks join, intersecting the surface to detach one or more particles from the contact surfaces, forming a pit or spall. After the appearance of a visible spall, propagation may be relatively slow or rapid, depending upon operating conditions, material characteristics and lubrication. Under certain conditions, the useful life beyond the first visible fatigue damage can be a large multiple of the life up to the initial spall formation.

For more information about the "Rolling Bearings Handbook and Troubleshooting Guide" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=21

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