Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1189076
HYDRAULICS drops to its recommended level. If the pre-charge is too low, the charging rig comes with a hose to connect it to a nitrogen bottle. With the nitrogen bottle connected, crack the valve on the bottle and slowly add nitrogen until the pre-charge reaches the desired level. e correct pre-charge varies by the application and type of accumulator. Most accumulators are the bladder, piston or diaphragm type. Follow any recommendations from the original equipment manu- facturer (OEM), if they are available. If not, the correct pre-charge can be estimated. When an accumulator is used for volume purposes, such as to apply a brake in the event of a power failure, to supplement the output of a pump, or to maintain a constant system pressure, most manufacturers recommend a bladder accumulator be pre-charged to 80 percent of the minimum acceptable pressure and a piston accumulator to 100 pounds per square inch (psi) below minimum pressure. Unfortunately, in many instances, the OEM pre-charge pressure is not available, and the minimum acceptable pressure is unknown. When this is the case, pre-charging to 50 percent of the maximum system pressure usually yields an acceptable result. e most common cause of an accumulator failure is too high of a pre-charge. If the pre-charge is higher than it should be, the bladder in a bladder accumulator will hit the poppet assembly during each cycle, causing either a cut bladder or excessive stress wear of the spring in the poppet. In piston accumulators, too high of a pre-charge can damage the piston and prevent it from hitting bottom at each cycle. Too low of a pre-charge (or an increase in system pressure without a compen- sating increase in the pre-charge) can also lead to 18 | November - December 2019 | www . machinerylubrication.com A charging rig should be used to pre-charge an accumulator. If the pre-charge is too high, the bladder in a bladder accumulator may hit the poppet assembly, resulting in a cut bladder or excessive wear of the poppet spring. If a bladder accumulator loses its charge, the bladder may be pushed to the top of the shell and become ruptured by the Schrader valve assembly. Nitrogen Bottle Connection Bleeder Valve Gas Chuck Handle Schrader Valve Gauge Bladder Poppet Valve Spring Shell