Accumulators for hydraulic system


Need of Accumulator

  • The components of a hydraulic system require a continuous supply of pressurized fluid. For example, a hydraulic actuator gets the work done on the load by converting the energy of the fluid into mechanical energy. 
  • In the absence of an accumulator, the hydraulic pump would be continuously running to cater to the need for valve operation. The pump will frequently start and stop, which affects the pump’s performance and its health. 
  • A hydraulic accumulator is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure that is applied by an external source of mechanical energy.
  • The accumulator stores energy which can be used in an emergency where there are no other means of power supply. It can be compared with the use of capacitors in electrical circuits. 
Types of accumulators:
  1. Gas-charged (nitrogen usually) (Hydro-pneumatic accumulators)
  2. Spring-loaded
  3. Weight loaded
Gas-charged accumulators: 
The gas-charged accumulators work on the principle of Boyle's law. Boyle's law states that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature. For more information, click here.
Boyle's law: Pressure (P)  is inversely proportional to volume (V) for constant temperature (T)
Relationship between Pressure and Volume

 Different types of gas-charged accumulators (separated type: separated type of accumulators use separation between gas and fluid):
  1. Bladder accumulator
  2. Piston accumulator
  3. Diaphragm accumulator
Bladder accumulator:
Bladder accumulator

Operation: 
  • Initially, the accumulator is pre-charged by filling gas (usually Nitrogen) inside the bladder. A fully charged bladder closes the poppet.
  • Stage I: When the system does not require hydraulic fluid: When the system does not require hydraulic fluid, the pressure inside the line increases, thereby increasing the pressure on one side of the accumulator. When the hydraulic pressure external to the accumulator (i.e., the pressure inside the line) is higher than the pressure inside the accumulator, oil from the hydraulic circuit is forced into the accumulator compressing the gas and thereby storing the energy in the compressed gas and also storing a reserved volume of fluid around the bladder.
  • Stage II: When the system requires hydraulic fluid: When the system requires hydraulic fluid, the pressure inside the line decreases. When the hydraulic pressure external to the accumulator drops below the pressure inside the accumulator, the compressed gas forces oil from the accumulator and the gas expands until the pressure internal to the accumulator equals the pressure internal to the accumulator
Piston accumulator: 
Piston accumulator
Operation: The operation of the piston accumulator is similar to that of the bladder accumulator. Here, the gas is filled inside the gas chamber which is exactly above the piston. A fully charged piston accumulator closes the hydraulic cap. When the pressure on either side of the accumulator changes, the oil is stored/discharge from the accumulator.
The diaphragm accumulator uses a diaphragm to separate the gas and fluid, while its operation is the same as that of the bladder accumulator.

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