Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/704613
14 | July - August 2016 | www.machinerylubrication.com valves can fail closed, which will maintain the pressurized oil in the accumulator. If a line is taken off or a component removed, an individual can become injected with high-pressure fluid. When a manual dump valve is used, the human factor enters the equation. At one plant, a young millwright was severely injured when he was injected with high-pressure oil after he failed to open the hand valve. There was no proce- dure in place for opening the valve before working on the system. Many times the gauge is located on the pump side of the check valve and not the accumulator side. When the pump is turned off, the gauge will drop to zero as the oil bleeds to the tank through the hydraulic pump's internal tolerances. The mainte- nance person or operator thinks the pressure is at zero and has no way of knowing if the pressurized fluid in the accu- mulator has been released. On systems of this design, a gauge should be installed at or near the accumulator. Mistake #3: Poor Troubleshooting Techniques In our hydraulic workshops, we stress that the quickest and easiest method of troubleshooting a machine is to use a hydraulic schematic. The response from students is usually one of the following: "Management won't give us time to trou- bleshoot," "We don't have or know where our schematics are," or "We don't know how to read the schematics." When a hydraulic problem occurs, infor- mation must be gathered to determine which component is causing the problem. A few examples include checking the pump case drain flow or checking for heat in the system. Many times the supervisor inter- venes and demands that the pump, cylinder or other component be changed. At one plant, a supervisor instructed a millwright not to troubleshoot but to manually actuate a directional valve. This resulted in an accumulator discharging into a partially filled 5,000-gallon reservoir. The top of the reservoir blew off, which shut down the mill for seven days. Hydraulic schematics are usually located inside the machine manufacturer's manual, which is often kept in a maintenance office or storeroom. When a hydraulic problem occurs, the last thing the maintenance person wants to do is to take 15 or 20 minutes to find the manual. After all, when a machine is down, time is money. A better option is to mount larger schematics by the system under a Plexiglas cover. Smaller prints can be laminated and similarly located. If the schematic is readily available, it will be used. The most common statement I hear from mechanics and electricians when consulting with a plant on a problem is, "I don't know much about hydraulics." This means they either have not been trained properly or have forgotten what they have learned. On the other hand, when I visit plants where machinery-specific hydraulic training has been conducted, I normally hear, "We use manuals and schematics all the time." Without the proper training, you cannot expect your maintenance crew to troubleshoot effectively. Mistake #4: Poor Hydraulic Reservoir and Oil Maintenance While most plants do a good job of maintaining system filters, the reservoir usually is not given any attention. When a system is designed, the reservoir size is factored into the amount of heat that will be removed from the system. Reservoirs should be cleaned a minimum of once a Most systems have a dump valve that allows high-pressure fluid in the accumulator to dump to the tank, permitting the pressure to drop to zero. Using a hydraulic schematic is the quick- est and easiest method of troubleshooting a machine. A hydraulic schematic is the quickest and easiest method of troubleshooting a machine. COVER STORY