Accumulator Precharge Pressure
Precharge is the pressure of the nitrogen filled into the accumulator before any oil enters, and it determines how much energy the element will store. The general rule is to select it at about 80-90% of the system's lowest operating pressure. Wrong precharge both lowers capacity and shortens bladder life.
If the precharge is too low the accumulator fills early, the usable volume drops and the bladder collapses to the bottom on every cycle. If it is too high the element engages late and does no work at all at low pressure; the bladder slams into the valve on every discharge. In both cases life is shortened.
- Measurement: done only after the hydraulic side is completely drained, with a charging kit and with the oil temperature close to ambient temperature.
- Temperature effect: nitrogen pressure changes with temperature; a value measured on a hot system shows the real precharge as higher than it is.
- Interval: checking at least once a year is common practice; 5-10% leakage per year is normal.
- Gas: only nitrogen is used; using oxygen or compressed air is dangerous.
In the field, on complaints of a spongy lever feel and irregular motion, accumulator precharge is one of the three items to check together with air leakage and deadband.
Where this term is used: Connect Plus and Minus, Run: Installation That Does Not Depend on Technical Staff