Pre-charge pressure can either be too high or too low causing operator problems or damage to accumulators. Below we have listed the common issues associated with over and under pressures on both Bladder and Piston type accumulators.
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Pre-charge pressure too high (or reduction in system pressure)
This may cause operational problems or damage to accumulators. With a piston accumulator the piston will travel too close to the hydraulic end cap and the piston could bottom out, reducing output and eventually damaging the piston and piston seal. The piston can often be heard bottoming, warning of impending problems. In a bladder accumulator the bladder can be driven into the poppet assembly when discharging. This could cause a fatigue failure of the poppet spring assembly, or even a pinched bladder. Excessive pre-charge pressure is the most common cause of bladder failure.
Pre-charge pressure is too low (or an increase in system pressure)
This can also cause operating problems and subsequent accumulator damage. With no pre-charge in a piston accumulator, the piston will be driven into the gas end cap and will often remain there. Usually, a single contact will not cause any damage, but repeated impacts will eventually damage the piston and seal. Conversely, for a bladder accumulator, too low or no pre-charge can have rapid and severe consequences. The bladder will be crushed into the top of the shell and can extrude into the gas stem and be punctured. One such cycle is sufficient to destroy a bladder. Overall, piston accumulators are generally more tolerant of incorrect pre-charging pressures.
Pre-charging too fast
If a bladder accumulator is charged too fast, high-pressure nitrogen, expanding rapidly becomes cold and chills the bladder. The chilled, brittle rubber, expanding rapidly could potentially rupture. The bladder could also be forced under the poppet and torn.