Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1005929
www . machinerylubrication.com | July - August 2018 | 19 ML malfunctions, the operator knows how the machine feels, sounds and runs. is individual usually has data displayed on a screen and understands when a pressure, position or other indicator is reading incorrectly. 3. Review the Schematic e best times you will spend troubleshooting is while reading and tracing a hydraulic schematic. Frequently, valves are inside mani- folds or located in out-of-the-way places. By following the lines on the schematic, you can often find the problem before the first part is changed out. Several years ago, I was flown to a plant in Arkansas that was having speed issues with a large stacker. e stacker was supposed to operate at fast and slow speeds. e problem was that it only operated in the slow mode of operation. When I arrived, several millwrights, electricians, supervisors and the plant manager were near the machine. I asked for a hydraulic schematic of the system. One millwright said, "We never use those because they're locked up in the plant engineer's office." I told him that this was one time we were going to need it because several of the valves were located on and inside a manifold. Once the schematic was found, I iden- tified one solenoid-operated valve that had to be energized in order for the stacker to lower. When the valve was manually actuated during the fast cycle, the stacker lowered quickly. e issue was a blown fuse on the solenoid-operated valve. e plant could have saved hours of downtime had it taken the time to troubleshoot from the schematic when the machine first went down. 4. System Trouble- shooting and Adjustments After you have identified the problem, gathered information and reviewed the schematic, you should verify that the system pressures are set properly. is includes the pump compensator, relief valve, pressure-reducing valves and other pressure-control va lves in the system. Also, ensure that all the accumulators are pre-charged with dry nitrogen. Many times an issue can be resolved by simply setting the pressures to the appropriate level. After one of my courses in Oregon a few years ago, a student asked me to look at a system that was running extremely hot. He wasn't exaggerating, because when the reservoir was photographed with an infrared camera, it revealed a temperature of 320 degrees F. I checked the tank line of the relief valve, which should have been at ambient temperature. However, I found a temperature of 340 degrees F. This indicated that the relief valve was stuck open or set below the compensator setting or that the pump's compensator spool was stuck. When the relief valve was set 250 psi above the compensator, almost immediately the temperature started dropping. Another issue detected in this system was that the accumulator manual dump valve was partially open, allowing oil to flow to the tank, generating heat. Twenty-four hours after the pressures were set and the dump valve was closed, the tempera- ture dropped to 132 degrees F. Once the pressures are set, make temperature checks throughout the system to confirm that no excessive bypassing is occurring. is can be done with an infrared camera or temperature gun. Typically, there are several tank lines in a hydraulic system that should be at ambient tempera- ture. These include manual and automatic accumulator dump valves, air bleed valves and relief valves used with pressure-compensating pumps. e suction line and case drain of a variable displacement pump should also be checked for excessive heat generation. It is important to record the temperature of the lines when the system is operating normally to establish a reference. It is important to verify that all system pressures are set properly. Use an infrared camera to check accumulators. Installing a manual valve in the line to a prepress ram helped troubleshoot a pressure problem at a plywood plant.