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Q & A

"Is it alright to mix an R&O hydraulic oil with an AW hydraulic oil in a hydraulic application?"

Mixing oils with different additive packages is never recommended. Doing so could compromise the additive performance of both constituents, cause corrosion of component surfaces and lead to increased mechanical wear. And, trending of some oil analysis properties will be compromised. In a pinch, if the oils are the same viscosity, you may be able to get away with mixing for a short time. If you must mix the oils or live with an accidental mixture until the next scheduled outage, take the following precautions:

1. Visually inspect for signs of sludging, poor demulsibility and foaming.

2. Increase the frequency of oil analysis to spot abnormal wear, corrosion or lubricant degradation.

3. Flush and change the oil as quickly as possible. A drain leaves 5% to 40% of the old oil in the system, therefore a flush will need to be performed.

4. Keep up the frequent inspections and oil analysis to be sure that the oil stabilizes.

Today's Tip

• To keep dirt out of greased bearings while relubricating, use a three-pronged approach:

  1. Use plastic caps that fit over the grease fittings to keep contamination out.

  2. Use a lint-free cloth or clean rag to wipe down the fitting prior to greasing.

3. Use Saran Wrap or some other type of clinging cooking wrap to cover the end of the grease gun when it is not being used.

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Book Bits

From "The Practical Handbook of Machinery Lubrication":

This section of the book identifies five reasons for regular oil drain intervals. Here's number one:

#1 - SELF GENERATION OF CONTAMINATION IN THE OIL. Every engine, hydraulic pump, gear set or other component very slowly wears as it operates, and these tiny, sub-micronic particles of such elements as iron and copper, become catalysts which slowly attack the oil, causing acids to form. These tiny metal contaminants, combined with carbon soot particles resulting from the combustion process in engines, also circulate in the system and through their abrasive action, create more wear. These solid particles become just like a fine grinding compound and will slowly scratch and score bearing surfaces, turbocharger bearings, crankshaft journals, cylinder liners, and hydraulic pump and valve surfaces.

Normal full-flow filters are generally rated at about 10 micrometers and 40 micrometers in hydraulic systems and engines respectively, and will not remove these sub-micronic particles.

Furthermore, if these filters become plugged, or if the by-pass valves within them remain open for long periods of time, such as at cold start up, contaminated oil will be pumped throughout the system.

It is important to remember that if the levels of self-generated contamination are allowed to increase until some damage by abrasion is caused, it will be too late to prevent more on-going damage, even if the dirty oil is drained.

For more information about "The Practical Handbook of Machinery Lubrication" go to:

http://www.noria.com/secure/product_detail.asp?catalogid=55

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