Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/704613
COVER STORY 16 | July - August 2016 | www.machinerylubrication.com year to allow some of the heat in the oil to be released to the atmosphere. On a log-loader in Ontario, the reser- voir had not been drained or cleaned in 17 years. A thick layer of sludge was found on the bottom of the tank once the oil was drained. A reservoir that is not cleaned can act as an incubator instead of dissipating the heat in the oil. Many reser voirs contain a suction strainer. This strainer is located under the oil level and is often out of sight and out of mind. It should be removed from the reser voir at least once a year and cleaned by blowing air from the inside out. The strainer should also not be over- looked when troubleshooting. If the strainer plugs up, cavitation of the pump will occur. One plywood plant changed five pumps on its debarker hydraulic unit. It finally drained the oil out of the tank and found a shop rag wrapped around the strainer. It should be noted that some strainers have a built-in check valve that allows oil to bypass when the screen is contami- nated. This is even more of a reason to clean the strainer regularly, because when in bypass, dirty oil will flow into the pump. Another common problem is adding unfiltered oil to the system. This should never be done. The oil that leaves the refinery might be clean, but by the time it is stored in transfer trucks and drums, it may only meet a 50-micron standard when added to the tank. Many systems have connections for attaching the fill pump hose so the oil in the drum is ported through the system filter before it enters the reservoir. A standalone filter cart can also be used when refilling the tank to remove contaminants. Mistake #5: Component Replacements Don't Have the Same Part Numbers When a hydraulic problem occurs, usually one component has failed. It is essential to match the part numbers between the new and old components. Hydraulic pumps and valves that look alike are not necessarily the same. Each number or letter in the part number indicates a feature about the pump or valve. If one letter or number is different, the manufac- turer's literature should be consulted to identify the difference. A few years ago, a plant had the main directional valve fail on its tilt hoist. The valve had the following part number: DG5S8- 2C-T-50. A local vendor was called who said he had a valve with the same spool configuration and mounting pattern in his central distribution center. The valve with the following part number was flown in and delivered to the plant the next day: DG5S8- 2C-E-T-50. When the valve was installed, the tilt hoist cylinders still would not extend and retract. The manufacturer of the valve was then called and given the two different numbers. The original valve (with the letter "E" omitted from the part number) was an internally hydraulically piloted and drained valve. The valve sent by the vendor was an externally piloted and internally drained valve. Since there was no external pilot line connected in the system, the new valve would not work. To solve the problem, the valve manu- facturer told the mechanic at the plant to remove the internal plug in the "P" port and install it in the "X" port. Once this was done, the tilt hoist operated normally but only after 18 hours of downtime. These common mistakes are made primarily because of a lack of knowledge. When a machine is down, the supervisor, mechanic or electrician is going to do whatever is necessary to get the machine back online in the shortest amount of time. By making sure these top five errors don't occur at your plant, you can reduce downtime, help your plant operate safely and improve hydraulic troubleshooting. This image shows a tilt hoist with a failed main directional valve. THESE COMMON MISTAKES ARE MADE PRIMARILY BECAUSE OF A LACK OF KNOWLEDGE.