Machinery Lubrication

Machinery Lubrication Nov-Dec 2019

Machinery Lubrication magazine published by Noria Corporation

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matches the system pressure, so any reduction in system pressure will cause the accumulator to discharge oil to the system. e accumulator thus will supplement the pump during portions of the cycle when the system demands more flow than the pump can provide. Over time, oil will bypass across the piston seals, displacing nitrogen at the top. e first indication of this is an increase in the pre-charge pressure when no nitrogen has been added. Because of the bypassed oil on top, the stroke of the piston is reduced. System pressure drops, stalls may be noted, and the piston can become damaged by repeatedly hitting the bottom of the accumulator. Oil can be removed from the top of the accumulator by attaching the charging rig and opening the bleeder valve with the system pressurized, removing all nitrogen and oil. When oil stops coming out, the piston is at the top. e system can then be shut down, the dump valve opened to drain oil from the bottom, and the pre-charge restored, recovering the accumulator's diminished capacity. If oil never stops coming out of the bleeder valve, the piston is badly worn and must be replaced. Mounting an Accumulator It generally is best to mount accumulators in a vertical position with a mounting bracket about two-thirds of the way up the shell. Mounting a piston accumulator horizontally will cause more rapid wear of the piston seals. Bladder accumu- lators can also be damaged if they are mounted horizontally. In addition to uneven bladder wear, fluid can become trapped away from the outlet if a cavity forms between the bladder and the shell. Diaphragm accumulators usually can be mounted in any position. Inspecting Accumulators Hydraulic accumulators should be carefully inspected visu- ally at least once per year, more often in environments unfriendly to steel. Ensure there are no rust spots or cracks in the paint. Look for loose mounting points, worn rubber and any indica- tion of movement during operation. Check all fittings for leaks. At least every five years, the accumulator should be removed from service and hydrotested. Finally, never attempt to repair an accumulator shell. If there are any breaches, the shell should be discarded and replaced. 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 operation and repair for the Central Intelligence Agency at American embassies overseas. 20 | November - December 2019 | www . machinerylubrication.com HYDRAULICS

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