Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1103301
www . machinerylubrication.com | March - April 2019 | 25 ML onto the ferry so vehicles could be driven aboard. Once the ferry had been loaded, the ramp was lifted, and the ferry proceeded to the island. After only a couple of months, signifi- cant vibration was observed. Before long, the ramp had to be shut down for fear the mechanical infrastructure would be damaged because it was twisting toward one side. Plans were made to replace one of the million-dollar cylinders after only a few months of operation. e representative from the Depart- ment of Transportation was now asking me whether I had an idea of anything else that could be causing the vibration? I agreed to help and asked if she could provide some schematics of the system. She emailed me a file with the schematic. e design was about what I expected. Downstream of the power supply and four-way directional valve, a flow divider and two cylinders were shown, similar to the illustration at the top of page 24. What I did not see on the schematic was a set of crossport relief valves at the flow divider. Often, crossport relief valves, while in place, may not be drawn on the schematic, so I asked her to verify their presence. It turned out the crossports had been omitted from the system, and the small difference in cylinder bypass had rendered them out of synch. I recommended a set of crossports be installed so when the first cylinder reached the end of its stroke, its associated crossport would open and allow the second cylinder to complete its stroke before stopping the move- ment of the ramp, as illustrated on page 24. Once the crossport relief valves were added, the cylinders synched up and all vibration ceased. A million-dollar cylinder replace- ment was avoided by installing a $200 set of crossports. Cautions and Recommendations If crossports are built into the f low divider, they likely will come facto- ry-adjusted. is will work fine for most applications, but they may not be as respon- sive as you would like. Actuator damage is also possible at high pressures because flow dividers have a tendency to amplify pres- sure to one side. Typically, when the flow divider and crossports are part of the original design, their recommended setting will be provided. In the absence of designer specifi- cations, I recommend the crossports be set approximately 200-400 pounds per square inch higher than the pressure required to move the heaviest load at each output of the flow divider. ML About the Author Jack Weeks is a hydraulic instructor and consultant for GPM Hydraulic Consulting. Since 1997 he has trained thousands of electricians and mechanics in hydraulic troubleshooting methods. Jack has also taught radio-wave propagation for the U.S. Air Force and telecommunications equipment opera- tion and repair for the Central Intelligence Agency at American embassies overseas. Gear-up for efficiency. Industrial gear oils are transformed with Evonik's NUFLUX™ technology. Geared for higher performance with lower formulation cost, Evonik additive technology provides a premium solution backed up by OEM approvals, industry standards and performance tests. With NUFLUX™ technology, you'll find a broad range of viscosity grades suitable for a variety of demanding industrial gear applications. The Oil Additives specialists at Evonik―Let it flow. www.evonik.com/oil-additives Find us at bauma 2019 Hall A3, Booth 244 K190133_EOA_NufluxGear_Anz_123_8x196_85mm_MachineryLubrication_RZ01a.indd 1 08.02.19 09:49