In This Issue:

• Up Front: Quick Reservoir Inspections

• Book Bits: Bearing Cleaning Tips

• Today's Tip: Experimenting With Grease Quantity

• Q&A: 100 Percent Filter Efficiency

Up Front

Quick Reservoir Inspections

What quick inspections can you incorporate into your routine machinery walk-downs to help enhance reliability?

For instance, when inspecting sight glasses for fluid level, do you check the color and clarity as well? Does the oil appear milky or too dark? Perhaps the level gauge or sight glass itself has become fouled with gummy deposits. This could indicate oxidation, varnish or sludge.

Are breather filters secure and in good working order? Is the breather soaked with oil? Does the breather element need to be changed? Is a dessicating breather required to control moisture ingression?

Is the outside of the machine clean (especially around inspection hatches and fill ports)? Most machines that are dirty on the outside are usually dirty inside as well. Is it sealed tightly to prevent entry of dirt and moisture?

I'd like to hear about the types of reservoir inspections you use and if you've had any 'saves' as a result of them. Send me an e-mail and let me know.

Mike Ramsey
mramsey@noria.com

Book Bits

From "Rolling Bearings Handbook and Troubleshooting Guide":

Bearing Cleaning Tips

After bearings operate for a period of time, they may develop deposits of lubricant varnish and contamination from the environment. Unused bearings may also become contaminated due to broken packages or dirty storage areas. In some instances, flushing the bearing with clean lubricant while it is in operation provides some cleaning.

When the bearings are very contaminated with dirt and sludge, soak them in kerosene, mineral spirits or special commercial solvents. Some solvents can be detrimental to nonmetallic cages, seals or other components. After cleaning with solvents, bearings are extremely vulnerable to corrosion or mechanical damage and should be protected or lubricated immediately. Handling with bare hands can corrode the bearing surfaces because of the acidic moisture on the hands. A clean, dry, unlubricated bearing can be easily damaged by the movement between rolling bearings and raceways. Such bearings should never be spun or subjected to shock or vibration before a coating of lubricant or preservative has been applied.

Click here for more information about "Rolling Bearings Handbook and Troubleshooting Guide".

Today's Tip

• When running grease-packed bearings at higher speeds (in excess of 5000 rpm), experiment with the quantity of grease in the bearing. A 10 percent change in the quantity of grease can drastically affect the amount of heat generated by the bearing (even as much as 40°F depending on how close to optimum you are). If there is too much grease for the bearing to push out to surrounding pockets, the bearing will heat up quickly. Often the optimum amount of grease is less than what you might think. Be sure to provide a sufficient run-in period for the bearing to position the grease before exposing it to full- time duty. (Tip submitted by Jason Moe, Woodward Governor Co. Thanks Jason!)

Each tip published will earn the sender $25. Click here to submit your tip.

Q & A

100 Percent Filter Efficiency

"What does industry consider the standard in regards to filter efficiency? When I hear that a filter is rated at 1 micron, does that mean it is 100 percent efficient at that micron size?"

Filter ratings are an often misunderstood area of contamination control. The most commonly used rating is the Beta ratio, which is defined as the ratio of the number of particles upstream of the test filter versus the number downstream, greater than a given size. Using the Beta ratio, a 3 micron filter with a Beta 75 rating, will have on average 75 particles larger than 3 micron upstream of the filter for every one 3 micron or greater particle.

The efficiency of the filter can be calculated directly from the beta ratio since the % efficiency is simply (beta-1)/beta x 100. A beta 75, 3-micron filter is thus said to be 98.66% efficient at removing 3 micron and larger particles. It is important to note that a change in the beta rating from 75 to 200 at the same micron rating represents an increase of less than 1% in efficiency, but the beta 200 filter is more than 3 times more effective at removing 3 micron and larger particles than the beta 75 filter.

Caution must be exercised when using beta ratios since they do not take into account field operating conditions such as pressure surges and changes in temperature, which can affect real life performance. A filters beta ratio also does not give any indication of its dirt holding capacity, the total amount of material that can be trapped by the filter throughout its life, nor does it account for how the capture efficiency changes over time. Nevertheless, beta ratios are an effective way of gauging the expected performance of a filter.

The ISO standard for Multi-pass filter testing (ISO 16889) has recently changed to require filter manufacturers to determine the average particle sizes which yield Beta ratios equal to 2, 10, 75, 100, 200, and 1000, again using the multi-pass test stand approach. The new standard gives a better interpretation of a filter's overall performance.

Of course, regular monitoring of fluid cleanliness using ISO particle counting should be used to determine the efficiency of the filter in actual field conditions.

Martin Williamson, Noria Corporation

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