Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1005929
20 | July - August 2018 | www . machinerylubrication.com Check the accumulators used for volume with an infrared camera. When cycling frequently, the bottom half or two-thirds of the shell should be hotter than the top half or one-third. e pre-charge pressure should be checked with a charging rig for accumulators that do not cycle regularly or that are used for shock and to maintain pressure. e key to troubleshooting pres- sure problems is to isolate various points in the system. Oil will always take the path of least resistance. If the machine is experiencing a pres- sure problem, then oil is most likely bypassing in the system. Recently, a ply wood pla nt was only building 1,400 psi in its prepress rams when 2,100 psi was required. The line to each ram was photographed with an infrared camera. e line to one ram was 142 degrees F, while the lines to the other three rams were 120 degrees. F. A manual valve was installed in the line to the ram that was hot. When the manual valve was closed, the pressure built up to the normal level of 2,100 psi. e problem was the prefill valve for that ram was stuck open, allowing all the pump volume to bypass back to the tank at 1,400 psi. Many times a va lve that is stuck open can be removed from the system to check for wear and conta mination. A few mont hs ago, the extruder motor on an injection-molding machine would not rotate at the proper speed. is indicated a volume problem in the system. Several tests were conducted, including insta lling flow meters to check the pump volume and inserting mechanical stops in the manifold valves to prevent them from opening. When removing one logic valve to install the mechanica l stop, the va lve was found to be stuck open. is valve was teed off the line to the hydraulic motor, which allowed the oil to bypass back to the tank. 5. Reliability Checklist W hen the issue is solved, the toolboxes are loaded up and everyone usually goes back to their normal duties. What should be done at some point in the near future is to develop a reliability checklist on the system. is list should consist of pressure and temperature read- ings, filter and breather conditions, oil cleanliness, condition of the hoses and clamps, current readings on the electric motor, voltages to proportional valves, etc. These checks should be made regularly to avoid unscheduled downtime. e recorded information will be a useful tool when future hydraulic issues occur. When a machine goes down, panic management frequently kicks in and parts start being changed. Often times the problem can be very simple. Several years ago, a press was down for five days because of an O-ring stuck in the drain line of a pressure-control valve. Hydraulic troubleshooting is a step-by-step process. By following the five steps in this article, you can become a hydraulic troubleshooter and not simply a parts changer. ML About the Author Al Smiley is the president of GPM Hydraulic Consulting Inc., located in Monroe, Georgia. Since 1994, GPM has provided hydraulic training, consulting and reliability assessments to companies in the United States, Canada, the United Kingdom and South America. Contact Al at gpm@ gpmhydraulic.com. A valve that was stuck open proved to be an issue in an injection-molding machine that would not rotate at the proper speed. HYDRAULICS