Hydraulic Accumulators and Bladder Design
(a) Two Functions of an Accumulator:
Hydraulic accumulators serve two primary functions within a hydraulic system:
- Energy Storage: Accumulators can store hydraulic fluid under pressure, acting as a reservoir of potential energy. This stored energy can be used to:
- Supplement Pump Flow: During sudden demands for hydraulic power, the accumulator can release stored fluid to meet the temporary surge in demand, reducing the workload on the pump.
- Dampen Pressure Shocks: Accumulators can absorb pressure spikes caused by rapid load changes or actuator movements, protecting other components from damage and providing smoother system operation.
- Maintaining System Pressure: In some applications, accumulators can help maintain a relatively constant system pressure, even during fluctuations in pump flow or demand. This can be beneficial for systems with sensitive components requiring consistent pressure.
(b) Gas Charged Diaphragm or Bladder Accumulator (Sketch and Description):
A gas charged diaphragm or bladder accumulator is a common type of accumulator that utilizes a flexible bladder to separate the hydraulic fluid from a compressed gas pre-charge. Here’s a description with a corresponding sketch:
Bladder Accumulator Hydraulic System
Components:
- Shell: A sturdy metal housing that contains the entire accumulator assembly.
- Hydraulic Fluid Port: The connection point for the hydraulic fluid to enter and exit the accumulator.
- Bladder: A flexible, gas-impermeable membrane made of high-strength elastomeric material. It separates the hydraulic fluid from the compressed gas.
- Pre-Charged Gas: Inert gas (typically nitrogen) at a predetermined pressure that fills the space above the bladder.
- Diaphragm (Optional): Some designs may incorporate a diaphragm plate to provide additional support for the bladder and prevent excessive bulging.
Operation:
- When hydraulic fluid enters the accumulator through the port, it pushes against the bladder, causing it to expand and compress the pre-charged gas in the upper chamber.
- The compressed gas provides a counterforce that balances the pressure of the incoming hydraulic fluid.
- As more fluid enters, the pressure within the accumulator increases until it reaches a predetermined level.
- When the demand for hydraulic fluid exceeds the pump’s capacity, the stored energy in the accumulator pushes the bladder back, releasing pressurized fluid back into the system.
- The pre-charged gas pressure determines the accumulator’s pre-charge pressure and influences the response characteristics of the accumulator.
(c) Preventing Bladder Extrusion:
To prevent the bladder from extruding or rupturing from the accumulator shell, several design features are employed:
- High-Strength Bladder Material: The bladder is made of a robust elastomeric material that can withstand high pressures and resist bulging or tearing.
- Pre-Charge Pressure Setting: The pre-charge gas pressure is carefully chosen to be lower than the maximum pressure rating of the bladder and accumulator shell. This ensures the bladder remains within its safe operating range.
- Diaphragm Support (Optional): Some designs utilize a diaphragm plate to provide additional support for the bladder, preventing excessive bulging and potential extrusion.
- Safety Features: Certain accumulators may incorporate pressure relief valves to automatically vent excess pressure in case of malfunctions, protecting the bladder from overpressure.
By implementing these design considerations, bladder accumulators can operate safely and reliably within hydraulic systems.