From "Wear Debris Analysis"

The condition of a machine cannot usually be determined from a single analysis of wear debris. Although an experienced user of the technique may form an opinion from the size of debris - large chunks undoubtedly conveying severe fatigue, for instance - a much clearer picture is conveyed only through trend analysis.

It would be extremely convenient if an absolute measure of wear debris were able to give a definitive go/no-go measure of condition. But this is only possible from experience built up from trend analysis on the same or similar machinery or systems. Many other types of condition monitoring also depend on this approach because of the wide variations in signal generation with condition. Trend analysis, however, is able to provide the required background for true machine condition determination.

More information about the book "Wear Debris Analysis"

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QUESTION: What is an ICP?

Get the answer.

"Many of the available side stream (portable) filter systems have low flow rates (> 4 gallons per minute), and I am concerned that it might not be circulating enough oil to get ahead of the contaminant level. What is considered to be a good target flow rate for side-stream filtration?"

There is no single answer for this question. Filter system selection must follow a thorough analysis of the system constraints and a clear definition of the task objectives. There are a handful of questions to ask about the targeted systems before selecting elements and hardware, including the following:

1. What is the relative cleanliness of the fluid in its initial state?

2. What is the new cleanliness target level?

3. How long can the portable filtration system run once it is put into operation?

4. What will the fluid viscosity be during filtration?

5. What is the sump volume?

6. What is the contaminant ingression rate?

The selection of filter elements and hardware can be a sliding scale based on the answers to these questions. A couple key principles to consider are:

1. If the flow is constant, as the operating viscosity increases, the element size should also increase.

2. As the flow increases element capture efficiency may decrease.

What does this mean in practical terms? Higher flow does not necessarily lead to improved cleanup rate unless the Beta (similar to capture efficiency) is not negatively effected. However, assuming Beta is constant, cleanup rate will be proportional to flow rate. For more on this check out this article from Machinery Lubrication.

Assume the following conditions: A) The facility is going to purchase a filter unit with a 5 GPM throughput; B) it will choose between a 5 inch spin-on, a 8.2-inch coreless element or the 16.9-inch coreless element; C) all the elements have the same beta rating (B10=100) regardless of flow rate; D) the facility has two 1,000-gallon sumps to filter; E) machine sump #1 has an operating viscosity of 180 cSt (circulating oil); and F) machine sump #2 has an operating viscosity of 55 cSt (hydraulic).

In this situation, any of the element options for sump #2 (hydraulic) may work, but the facility would be better off to select the 16.9-inch media for sump #1. The larger filter element will help maintain the 5 GPM rate (even positive-displacement pumps don't have 100% volumetric efficiciency) regardless of fluid temperature, which correlates to the amount of time the technician will have to leave the filter in place to reach the cleanliness target. Additionally, large filters translate to lower element flow density which typically translates to better filter economy (cost to take out a gram of dirt) and more stable capture efficiency throughout the filter's life.

The point of this exercise is to show that there are many factors that should be considered prior to making this decision. It is not a complicated decision if the objectives and the constraints are clearly defined. Start by evaluating the constraints and setting the cleanliness objectives. From there, it is a simple engineering exercise that can be rooted in known criteria. Read more about this topic.

Mike Johnson, Noria Corporation

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