Machinery Lubrication

Machinery Lubrication July Aug 2013

Machinery Lubrication magazine published by Noria Corporation

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AS I SEE IT circulation, which is not available from wetsump lubrication alone. The only alternative would be to use periodic portable filter carts to clean the oil and flush the sump. Onboard filtration is far superior and should be included in both constant-level and off-line circulation. Filtration offers the added benefit of being able to draw down contaminant levels even when the machine is at rest. Live-Zone Oil Sampling Obtaining a representative oil sample from non-circulating systems is always challenging. Circulation homogenizes the oil so that samples contain contaminants, wear debris and oil properties that are consistent with the current conditions of the machine and the oil. Oil analysis data is always more reliable from live-zone samples compared to those from static or noncirculating fluids. Oil Volume Benefits A constant-level circulation system includes a small external reservoir (see Figure 2). This reservoir fluid is added to the circulation loop along with the pre-existing system with an external reservoir can be used in place of an off-line circulation system to reap the benefits of greater oil volume. Oil Cooler/Heater Option Where needed, an oil cooler or heater can be installed in the circulating system. Magnetic Plug Option Figure 3. An example of a commercially available constant-level circulation system that can be retrofitted to a conventional wet-sump machine. (Ref. Dodge-Rockwell) The periodic inspection of magnetic plugs to assess abnormal wear conditions is dramatically improved if the plugs are installed on circulating lines rather than sump drain ports. Minimal Risk of Sediment and Free Water Circulating oil interferes with settling zones that allow sludge and sediment to gather. Instead, these contaminants are trapped in the filter. Many wet-sump systems accumulate more sediment in the sump than oil, a condition that is nearly impossible to see. Sediment can be suddenly disturbed by machine movement, oil turbulence and oil drain-and-refill activities. This disturbed sediment, referred to as the fishbowl effect, can relocate to critical zones in the machine and induce suddendeath machine failure. Circulating oil also releases water vapor into the atmosphere more effectively. Conversely, simple wetsump systems allow water to puddle on the sump floor over time. Online Sensor Installation Figure 2. This is an illustration of a constant-level circulation (CLC) system. sump fluid. Filters and piping also add fluid to the circulating system. When, for example, you have twice as much fluid, you have twice as much additive (additives are sacrificial), half as much contaminant (per liter or gallon), half as much wear metal, half as much thermal damage to the oil and an overall lower oil temperature. The benefit from twice as much oil typically will translate into tripling the oil change interval (and all the hidden costs of an oil change). Keep in mind that a constant-level circulation 4| July - August 2013 | Circulating oil is far superior to static oil when it comes to mounting online oil sensors. These optional sensors can monitor viscosity, wear debris, particle counts, moisture contamination and other fluid properties. New Oil Filtration When new oil is added to a wet sump, it typically is not filtered and usually comes from a dirty transfer container. When filters are installed on constant-level circulation systems, all oil entering the sump must pass through the filter (single-pass filtration). This ensures a greater degree of contamination control where there is uncertainty about new oil cleanliness. Off-line circulation systems can also be fitted with quick-connects and valves so that new oil is pumped into the sump through the filter mounted in the off-line loop. What It All Means Not all machines need oil circulation. However, many would benefit greatly if circulation was provided (see Table 1). In my opinion, the best candidates are machines that are configured with wetsump lubrication and are prone to failure and/or are mission critical (high downtime and/or repair cost). Often these are the machines with the largest sump volume (e.g., 20 gallons or more). Many filter companies and fluid power distributors can supply these products. High flow rates generally are not required, which reduces the hardware and installation costs. When you add it all up, the benefits can substantially outweigh the retrofit costs. About the Author Jim Fitch has a wealth of "in the trenches" experience in lubrication, oil analysis, tribology and machinery failure investigations. Over the past two decades, he has presented hundreds of courses on these subjects. Jim has published more than 200 technical articles, papers and publications. He serves as a U.S. delegate to the ISO tribology and oil analysis working group. Since 2002, he has been director and board member of the International Council for Machinery Lubrication. He is the CEO and a co-founder of Noria Corporation. Contact Jim at

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