Controlling leakage is an important part of any lubrication program. Here is a list of potential causes of leakage:

• Design/Selection - through improper selection, sizing and tolerances of elements; improper closure of the clearance space between two mating or close running elements; improperly selected seals; use of defective, incompatible or highly porous material, and being unaware of what operational conditions might be imposed on the system.

• Manufacturing - through inadequate control over tolerances, mating of elements, surface finishes, material composition and foreign matter, assembly and quality. 

• Operation - through over-pressurization, over-loading, over-speeding, high dirt ingression, high temperature, fluid dilution, etc.

• Maintenance - through ineffective maintenance practices and strategies; not recognizing the signs of conditional failure, etc.

More Great Tips - From the Message Boards

The Practicing Oil Analysis Message Boards are a great place to express your opinions, get your questions answered, share experiences and make friends.

We've gleaned the Message Boards for useful information and found some great information on greases to share with you.

Actually, it doesn't change the 'viscosity', but rather the consistency of the greases. Greases are made up of a base-oil and a thickener. The base-oil has its own viscosity, and that is what forms the lubricating film in the application. The thickener serves to hold the oil in place where the lubrication is desired, and keeps out contaminants.

When incompatible greases are mixed, the consistency usually decreases, making the mixture softer. This may make it less effective at keeping the grease in the area needing lubricant. Also, the oil may 'bleed' out of the grease in such a mixture, leaving behind the thickener, which can harden. The hardened thickener may prevent subsequent shots of grease from reaching the bearing. Without the oil, the thickener is ineffective at lubricating the bearing and lubricant starvation failure can

The incompatibility charts are meant as a guideline. If you have mixed incompatible greases, or are considering doing so, the best thing to do is to mix up a batch of the two greases in the ratio anticipated and compare qualities. ASTM cone penetrating test and dropping point tests can be performed, or you can get a quick idea by using a tongue depressor and comparing the stiffness of the grease mixture to the unmixed greases. You can also put a dab of the mixture alongside dabs of the new greases and inclining the surface to check for excessive bleed.

Always avoid mixing unlike greases, but if it is unavoidable, some of these techniques may help you decide the proper course of action.

DAILY TIPS

• Viscosity Index (VI) is determined from viscosities measured at 40 and 100 degrees C (100 and 210 degrees F). Typically, the VI is then found from standard VI tables.
• Proper baffling is an important part of hydraulic reservoir design. Oil residence time in a reservoir influences air and water separation efficiency. With baffling, the oil is forced to remain in the reservoir longer, improving water shedding and air detrainment.

MORE GREAT TIPS

Today we are going to look at an excerpt from Dr. E. C. Fitch's book "Proactive Maintenance for Mechanical Systems." This passage is extracted from the fluid chemical stability section and describes some of the best methods for determining oxidation in equipment:

"Once the oxidation process occurs, five major changes in the oil result in the following:

1. Color becomes darker - changes from transparent or translucent in color to some degree of discoloration toward the point of complete opacity.

2. Odor becomes pungent and acetic due to the presence of excessive organic petroleum acid and similar products of oxidation.

3. Acidity increases - changes from a Neutralization Number from 0.06 to 0.12 KOH mg/g to well above 2.0 can occur.

4. Viscosity increases - the viscosity of an oil frequently may double or triple due to oxidation. Oxidative thickening is capable of producing fluids that have the consistency of molasses-like sludge under high operating temperature conditions.

5. Insolubles precipitate (sludging occurs) - after an induction period, the deterioration of an oil gradually accelerates until the formation of organic acids or deposition of sludge completely destroys the oil.

DAILY TIPS

• The Water Washout Test (ASTM D1264) is one way to measure the tendency of grease to withstand water washout in bearings. A ball bearing is rotated at 600 rpm; while 100ºF water flowing at five cubic centimeters per second impinges on the bearing housing. The test measures the percent of grease washed out in one hour. The test is repeated with 175ºF water.

• The three steps of proactive maintenance are:

1. Define the target root cause property (i.e., cleanliness level)

2. Achieve the target (i.e., improved contamination control)

3. Monitor (measure) the property regularly

MORE GREAT TIPS

Today we are going continue our series of excerpts from Dr. E. C. Fitch's book "Proactive Maintenance for Mechanical Systems." This passage is extracted from the fluid chemical stability section and describes some of the best methods for determining oxidation in equipment:

"A slight discoloration of the oil is nearly always present during the initial stages of oxidation. This discoloration increases as the process continues and the decoloration is accompanied by a drop in interfacial surface tension and a rise in viscosity, specific gravity and the neutralization number.

The rise in viscosity and acidity are not necessarily interdependent.

"Primary oxidation will cause a rise in acidity which will ultimately level off, at which point the viscosity may rise at an extremely rapid rate. Such increases in viscosity rate usually occur due to the generation of oxidation products of high molecular weight, held in fluid suspension. Paraffinic base

oils are less apt to produce sludge at an earlier stage as those of a polynapthenic base."

"The oxidation rate and the degradation products increase not only with increasing temperature, but also with increases in agitation (turbulence) and contamination - air, water, metallic particles, dirt and dust. The oxidation stability varies not only with the viscosity grade of the oil but also with the quality of the base stock. In addition, the actual base stock

from which the hydraulic fluid was derived and refined also affects the rate of oxidation."