Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1189076
16 | November - December 2019 | www . machinerylubrication.com Hydraulic accumulators are found in almost every industrial plant. Most facilities have several of them, but they often are misunder- stood. Accumulators can be the most dangerous hydraulic components in the mill, not because they are inher- ently dangerous, but because of the lack of understanding. All hydraulic accumulators, regardless of their purpose, store energy and therefore must be treated with some measure of respect. Accumulator Functions A hydraulic accumulator is used for one of two purposes: either to add volume to the system at a very fast rate or to absorb shock. Which func- tion it will perform depends upon its pre-charge. If the accumulator is to be used to add volume to the system, its pre-charge must be somewhat below the maximum system pressure so oil can enter it. If the accumu- lator will be used to absorb shock, it must be pre-charged close to the maximum system pressure so there will be little or no oil in it. Pre-charging an Accumulator An accumulator typically is pre-charged with dry nitrogen. Nitrogen does not react unfavorably with hydraulic oil under pressure, and since it composes nearly 78 percent of the earth's atmosphere, it is the least expensive gas that can be used safely. e next most plentiful inert gas is argon, which makes up less than 1 percent of the earth's atmosphere. Under no circumstances should an accumulator be pre-charged with oxygen or air. If compressed oxygen or air encounters even a small amount of any hydrocarbon, it can react violently, resulting in an explo- sion, fire, injury to personnel and property damage. An accumulator should bear a safety sticker that warns against pre-charging with any gas but nitrogen. New accumulators come with such stickers, but they often are scratched off or painted over. A charging rig should be used to pre-charge an accumulator. e pre-charge should be performed with no oil in the accumulator. Release any pressure at the accumu- lator inlet. Most accumulators have a dump valve that can be opened to drain oil to the tank. Screw the charging rig onto the accumulator's Schrader valve and turn the gas chuck handle clockwise to depress the pin. e current pre-charge can then be read on the charging rig. If the pre-charge is too high, a bleeder valve on the charging rig can be opened to release nitrogen to the atmosphere until the pre-charge Guidelines for Understanding and Maintaining Hydraulic Accumulators HYDRAULICS Jack Weeks | GPM Hydraulic Consulting "All hydraulic accumulators, regardless of their purpose, store energy and therefore must be treated with some measure of respect." 16 | November - December 2019 | www . machinerylubrication.com