Machinery Lubrication


Machinery Lubrication magazine published by Noria Corporation

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Page 23 of 80 | July - August 2017 | 19 momentarily increases to the "2A" valve setting, the spool will shift open and port the pressurized fluid through the directional valve and back to the tank. When the pressure drops below the "2A" setting, the valve spool will shift closed and the motor will start rotating. When the directional valve solenoid is de-ener- gized to stop the motor, the valve spool will shift to the closed center position (Figure 5). The motor will tend to continue rotating due to the inertia of the moving load and momentarily turn into a hydraulic pump, delivering oil to its outlet port. The pressure will build until the setting of the "2B" crossport relief valve is reached. The "2B" valve will then shift open and direct the oil flow back to the motor's inlet port. The setting of the "2B" spring will determine how fast the motor will come to a stop. If you're experiencing shock and leakage issues with hydraulic motor circuits, first verify that the crossport relief valves are located in the system. I have seen some systems where they have been omitted, allowing the shock to be taken out in the lines, hoses and fittings, which results in leakage. Secondly, make sure the crossport relief valves are properly set. When there is a problem in a hydraulic system, usually the first course of action is to turn up the pressure. Thirdly, the crossport relief valves should be located as close as possible to the hydraulic motor. A plywood plant in North Carolina was having a problem shearing the motor shaft off its rotary log-kicker hydraulic motor. As the logs came down the conveyor, the motor rotated and kicked the log off the conveyor and onto the infeed conveyor to the lathe. Upon inspection, the crossport relief valves were found in a block under- neath the directional valve, which was mounted 30 feet away from the motor. An additional set of crossport relief valves was installed near the motor, which eliminated the shearing of the motor shafts. Likewise, by using these three remedies, you can greatly reduce the hydraulic shock in your systems and help to eliminate oil leakage at your plant. 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 ML © 2017 Beckman Coulter, Inc. Beckman Coulter, the stylized logo, and the Beckman Coulter product and service names used herein are trademarks or registered trademarks of Beckman Coulter, Inc. in the United States and other countries.

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