Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/147079
Step 11 Flushing Tactics There are a lot of different ways to flush out a machine. You want to match the flushing method to the flushing condition. Following are common tactics for accomplishing this: Drawdown Filtration/Separation — Contaminants or insoluble suspensions removed by filtration or separation technologies at normal flow rates. High Turbulence, High Fluid Velocity, Low Oil Viscosity — Flushing is enhanced by high turbulence flushing conditions by lower flush oil viscosity and increasing oil flow rates. High Flush Oil Temperature — This reduces viscosity, increases turbulence and increases oil solvency. Temperatures in the range of 175 to 195 degrees F are generally targeted. Cycling Flush Oil Temperature — Using heat exchangers and coolers to change temperature during flushing across a 100 degree F range helps dislodge crusty surface deposits. Pulsating Flush Oil Flow — Rapidly changing flow rates by pulsation help dislodge contaminants from nooks and crannies. Pneumatic Vibrators and Hammers — Used to break loose debris from pipe walls and connectors. Sparge Flush — Air or nitrogen is bubbled into the flush fluid to improve cleaning effectiveness. Reverse Flush Oil Flow — By changing fluid flow direction, some contaminants and surface deposits can be dislodged and washed away. Wand Flush Tool — Used for wet sumps, gearboxes and reservoirs with access hatches and clean-out ports. A wand on the end of a flushing hose is used to direct high-velocity oil flow to loosen deposits or for picking up bottom sediment. Charged Particle (Electrostatic) Separators — Some suppliers have demonstrated success at removing varnish from machine surfaces and stripping out submicron soft contaminants that can contribute to varnish and sludge. Solvent/Detergent Flush Fluid — Various solvents and detergents have been used with different degrees of success, including mineral spirits, diesel fuel, motor oils and detergent/dispersant packages. Chemical Cleaning — These are chemically active compounds, typically caustics and acids, used to aid in the removal of organic sludge and oxide deposits. Mechanical Cleaning — This involves the use of scrapers, brushes and abrasives, typically used with solvents and other chemicals, to remove hard adherent surface deposits. The sampling frequency should be increased until you are confident that the system fluid is stable. Some adherent machine deposits require tactics that are more aggressive than a high-velocity flush, so you must match the flushing tactic and strategy to the problem you are trying to resolve with the flush. Once you understand the problem within the machine that needs to be cleaned, you can then select the appropriate flushing tactic to remedy it. This issue was described in Jim Fitch's three-part series on flushing for Machinery Lubrication, which can be read at www.machinerylubrication.com/Read/609/ oil-flush, www.machinerylubrication.com/Read/634/oil-flushingtactics and www.machinerylubrication.com/Read/657/flushing-oil. At this point, it should be obvious that a fluid changeout is not just a drain-and-fill operation. Care must be taken to confirm that the system is as clean as possible prior to introducing the new fluid. Most changeover procedures suggest that some of the old fluid will need to be either drained off the bottom or skimmed off the top of the reservoir after a period of time. Just because the changeover has been completed does not mean that you are "out of the woods." Your system will need to be closely monitored for a while to make certain that the flushing was thorough. Taking the time to verify that the system is fully flushed and purged of the old fluid prior to introducing the new fluid will go a long way toward ensuring a healthier hydraulic system. References Odden, Tom. (2001). "Cleaning and Flushing Basics for Hydraulic Systems and Similar Machines." Machinery Lubrication. Ruble, Lyle. (2006). "A Guide to Converting Hydraulic Systems from Mineral Oil to Synthetic Hydraulic Fluid." MRL Hydraulics. About the Author Loren Green is a technical consultant with Noria Corporation, focusing on machinery lubrication and maintenance in support of Noria's Lubrication Program Development (LPD). He is a mechanical engineer who holds a Machine Lubrication Technician (MLT) Level I certification and a Machine Lubricant Analyst (MLA) Level I certification through the International Council for Machinery Lubrication (ICML). Contact Loren at lgreen@noria.com. Step 8 Refill the reservoir to 75 percent and run the system in five-minute intervals. At each shutdown, bleed the air from the system. Pay close attention to the system sounds to determine if the pump is cavitating. Step 9 Run the system for 30 minutes to bring it to normal operating temperature. Shut down the system and replace the filters. Inspect the reservoir for obvious signs of cross-contamination. If any indication of cross-contamination is present, drain and flush the system again. Step 10 After six hours of operation, shut down the system, replace the filters and sample and test the fluid. From page 30 www.machinerylubrication.com | July - August 2013 | 17