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Hopefully, you have had a chance to examine at least one machine and develop a concept of the system and how important it is to maintain it. Let’s pick up where we left off and address the other oils in your machine tools. Main Hydraulic Systems Main hydraulic systems generally consist of a reservoir, intake strainer, pump, in-line filter, pressure switch and gage, distribution lines, valves, flow restriction devices, check valves, and cylinders. Even though there seem to be many components to be concerned about, performing a preventive maintenance inspection is fairly simple. Most hydraulic systems are considered closed-loop systems: what goes out should come back in. Before starting your physical inspection of this system, refer to your daily PM checklist and review the recent history of the system. If no oil has been added and the oil level in the reservoir is good, your inspection will be quick. However, if there is a history of oil being added, this signals that there is a leak somewhere in the system. Checking for Leaks The easy part of this PM is spotting leaks. Due to the high pressure of the main hydraulic system (anywhere from 400 to 2,000 psi), oil is forced out of any leaks quickly, making them easier to identify. The tough part is uncovering the hydraulic components for inspection. The components are located throughout the machine, and, if the leak is slight, you may not find it until it gets worse. The way I approach this problem is to activate each hydraulic component while watching the system pressure gage. If the pressure dips abnormally low during activation or the pump whines hard, that particular system needs to be uncovered and activated again to look for oil seepage. (Note: Most cylinder shafts will have a light film of oil on them. This is normal. However, there should not be enough oil to cause any dripping.) If you do not notice any abnormalities during system activation, the entire system will have to be inspected until the leak is found. Routine PM If there is no documented history of oil being added, the system is easy to inspect. Your machine tools should have a chart in the manual indicating how often the oil needs to be changed. You can automatically change the oil or I recommend contacting your local oil distributor and have them sample all your oils a month prior to the scheduled PM. With the ever-rising cost of oil (hydraulic oil can cost anywhere from $15 to $40 per gallon), it is very expensive to throw oil away just because the manual says so. Most oil distributors provide this service without cost. A routine PM on the main hydraulic systems includes these steps:
Next month we will get into cooling systems. In the meantime, try to go through a system or two and e-mail your comments and questions to me. In an upcoming column, I will address your specific questions on the areas we have addressed so far this year. Talk to you next month. Mike Breen, a Certified Electronic Engineer, started his career as an aircraft electrician in the US Army, 101st Airborne Division. Mike’s 14 years of experience in machine tool repair include six years as a Field Service Engineer, his current position at Ellison Machinery Company of Wisconsin. He has engineered and set up complete preventive maintenance programs for many successful companies, resulting in significant increases in machine performance. - June 2000 |
Last month we discussed
the central lube system.