Precautions for Restarting Bladder and Diaphragm Type Bladder Accumulators

When adding air to bladder and diaphragm type accumulators, nitrogen must be introduced very slowly. If high-pressure nitrogen expands rapidly when allowed into the bladder, it can cause the polymer material of the bladder to cool at certain points, leading to damage-prone failures. Even with rapid charging, the bladder can be pushed into the conical section at the oil end, where the bladder may be sheared off.

If the pre-charge pressure is too high or the system pressure drops too low, and the pre-void pressure is not correspondingly reduced, the operation of the accumulator will be affected, leading to damage. Over-pressurization of the bladder with gas during evacuation can force the conical valve or bladder to rupture when the bladder is fitted with an air chamber. This is a basic cause of bladder failure.

Even without adding low or pre-charge air, excessive frequency variation in a bladder capacitor can cause wrinkling and rupture of the bladder dome under system pressure. This is the condition where the bladder is pushed into the air valve or punctured. In this case, a single cycle can destroy the bladder. Similarly, pre-charge pressures that are too high or too low can cause the piston of a piston accumulator to reach the bottom of its travel, damaging the piston and its seals. The good news is that if this happens, an audible warning will be produced.

In other words, piston accumulators can be damaged by improper air charges, but they are more tolerant than bladder accumulators. Pulsating flow from a pump can cause pressure pulsations, making the motion of the actuator uneven and producing vibration and noise. If aaccumulator sensitive to reaction and with low inertia is connected in parallel at the pump outlet, it can absorb flow and pressure pulsations, reducing noise.