Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1032074
22 | September - October 2018 | www . machinerylubrication.com ere is a lot to be said for reactive mainte- nance. "If it ain't broke, don't fix it!" is a common refrain across the country. In many of our hydraulic classes, the students tell us that their supervisors will not give them the time for many of the preventive maintenance techniques we teach. Naturally, as hydraulic consultants, we advocate a more proactive routine of maintenance than what we usually find in the facilities we visit. It's not that we don't understand the demands of real-world industrial settings. We understand them all too well. Our livelihood depends upon it. We know that much of a maintenance professional's time is spent putting out fires and that preventive maintenance must be sacri- ficed at times in favor of continuing production. But we also know that a machine behaving strangely is a machine that will soon transform from an asset to a liability. e trick is to know when to just leave it alone and when to intervene. ere are a few times when not taking action will almost definitely result in machine failure. Moving Too Slowly When a machine moves more slowly than it used to, it's not just tired. A reduction in speed means a reduction in flow. Either the pump isn't delivering as much flow as it used to or the flow it delivers isn't getting to the actuator. ink about how a hydraulic component fails – it leaks. Either it leaks onto the floor, in which case the problem is obvious, or it leaks internally, a condition called "bypassing." Find the bypassing component and you will find your speed problem. Ignore it and you will find yourself with lost production time. If it's the pump that is bypassing, it will need to be replaced. But don't replace it right away just to "see if that will fix it." ere are some quick ways to check the pump to determine its condition. e easiest way to check an electrically driven fixed-displacement pump is to measure the current draw of the electric drive motor. e following formula can be used to determine the horsepower required to drive a pump: Electric motor horsepower=gallons per minute x pounds per square inch x 0.00067. is formula provides for 13 percent more horsepower than what is required hydraulically. is is necessary due to the mechanical and heat losses in the pump. If you have a pump that supplies a volume of 30 gallons per minute (GPM) and the maximum system pressure is 3,000 pounds per square inch (PSI), the elec- trical horsepower can be calculated as follows: Electric motor horsepower=30 GPM x 3,000 PSI x 0.00067, or electric motor horsepower=90,000 x 0.00067, or electric motor horsepower=60.3. You then can check the nameplate data on the elec- tric motor for the full load current for a 60-horsepower motor. e average full load current for a 460-volt motor Proactive vs. Reactive Hydraulic Maintenance HYDRAULICS Jack Weeks | GPM Hydraulic Consulting "By checking your systems on a regular basis, you'll often find a failing component before it causes a shutdown of the machine." The case drain of a variable-displacement pump prevents pressure from building against the shaft seal. Case Drain 1,200 PSI 800 PSI