Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/147079
Oil Flushing PERSPECTIVE LOREN GREEN | NORIA CORPORATION 11 Simple STEPS for FLUSHING a Hydraulic SYSTEM I was recently asked about a procedure for flushing hydraulic systems in order to change from one type of fluid to another. Among the ideas mentioned involved using brake cleaner, diesel fuel or some type of acid cleaning. However, brake cleaner includes a number of chemicals such as acetone and tetrachloroethylene. These solvents are known to cause problems for nitrile, neoprene, millable polyurethane and silicone seals. Ethylene-propylene (EPDM) seals have a very poor petroleum oil and solvent resistance, and are not recommended for exposure to aromatic hydrocarbons or diesel oil. Therefore, depending on the types of O-rings and seals in your hydraulic system, the solvents used in brake cleaner and diesel fuel can dry out or damage your system's O-rings. There is also the issue of compatibility with the new type of fluid that has been chosen. In his article for Machinery Lubrication titled "Cleaning and Flushing Basics for Hydraulic Systems and Similar Machines," Tom Odden outlines the procedure for thoroughly cleaning a hydraulic system. This would be the only "one-size-fits-all" solution and an example of best practices. It involves mechanical and chemical cleaning of both the components and the system. Of course, not everyone is going to do a complete teardown along with a chemical and mechanical cleaning of each component and the system each time a fluid changeover is performed. So let's examine what should be done at the bare minimum to clean a hydraulic system. 28% of lubrication professionals say mechanical cleaning is the flushing method used most frequently at their plant, according to a recent poll at machinerylubrication.com) Step 1 While the fluid is at operating temperature, completely drain the system, paying attention to the reservoir, all lines, cylinders, accumulators, filter housings or any area of fluid accumulation. Also, replace the filters. Step 2 With a lint-free rag, clean the reservoir of all sludge and deposits. Make sure the entire reservoir is free of any soft or loosened paint. 16 | July - August 2013 | www.machinerylubrication.com Step 3 Flush the system with a lower viscosity fluid that is similar to the fluid to be used. A Reynolds number between 2,000 and 4,000 should be selected to achieve enough turbulence to remove particles from the lines. Stroke valves frequently to ensure they are thoroughly flushed. The fluid should be filtered and the flushing should continue until reaching one level beyond the system's target cleanliness levels. For example, if the target is ISO 15/13/11, continue to flush the system until ISO 14/12/10 is reached. Flushing is not about cleaning the fluid but rather about cleaning the machine. Step 4 Drain the flushing fluid as hot and as quickly as possible. Replace the filters and inspect/clean the reservoir again. Step 5 Fill the system to approximately 75 percent with the fluid to be used. Bleed/vent the pump. If the pump has a pressure relief or bypass, it should be wide open. Run the pump for 15 seconds, then stop and let it sit for 45 seconds. Repeat this procedure a few times to prime the pump. Step 6 Run the pump for a minute with the bypass or pressure relief open. Stop the pump and let it sit for a minute. Close the bypass and permit the pump to operate loaded for no more than five minutes. Allow the relief valve to lift to confirm that it is flushed as well. Do not operate the actuators at this time. Stop the pump and let the system sit for about five minutes. Step 7 Start the pump and operate the actuators one at a time, allowing fluid to return to the reservoir before moving to the next actuator. After operating the final actuator, shut down the system. Keep an eye on the fluid level in the reservoir. If the level drops below 25 percent, add fluid and fill to 50 percent.