Accumulators are simple devices that store energy in the form of fluid under pressure.
Types of Hydraulic Accumulators
- Weight loaded accumulators
- Spring-loaded accumulators
- Gas loaded accumulators
- Bladder type
- Diaphragm type
- Piston type.
Weight Loaded Accumulator
Advantages of Weight Loaded Accumulator
- Pressure remains constant for the full stroke.
- It can supply a large volume of fluid under high pressure.
- Limitations of weight loaded accumulator
- They are bigger in size and much bulky as compared to others of the same capacity. They consume more space and need heavy structures to support them.
Applications of Weight Loaded Accumulator
Spring Loaded Accumulator
Advantages of Spring-loaded accumulator
- With the use of multiple springs, a compact size accumulator can be developed for the same pressure as compared to the deadweight type accumulator.
- All parts are enclosed in a casing and no moving parts protrude out.
Limitations of Spring Loaded Accumulator
- The pressure exerted on the fluid is not constant as in the deadweight type. As the springs are fully compressed, the accumulator pressure reaches its peak and as the spring approaches their free length, the accumulator pressure drops to a minimum.
- Due to the presence of springs in the upper part of the cylinder, the useful piston stroke is limited. Hence accumulator cannot provide higher volumes.
Applications of Spring Loaded Accumulator
Non-separator type Gas Loaded Accumulator
A gas-charged accumulator pressurizes the fluid by the pressure of the gas. Gas loaded accumulators are also called as hydro-pneumatic accumulators.
When there is a separator placed between hydraulic fluid and gas, it is called separator type and when there is a barrier placed between hydraulic fluid and gas, it is called gas loaded accumulator with separator.
|Non-separator type gas loaded Accumulator|
As the fluid is charged in the shell, the fluid level rises, resulting in compression of the gas. The compression of gas induces pressure in it and this pressure exerts a force on the fluid surface.
Advantages of Non-separator type gas loaded Accumulator
- No mechanical elements to apply force on hydraulic fluid, hence simple in construction.
- It can absorb shocks and fluctuations since gas is easily compressible.
- Low operating cost.
Limitations of Non-separator type gas loaded Accumulator
- Due to a lack of physical separator, the gas may be absorbed in the oil. This makes oil compressible leading to the jerky motion of actuators.
- It must be always kept in a vertical position to confine gas at the top.
- The pressure on the fluid goes on decreasing as the volume of gas goes on increasing.
Applications of Non-separator type gas loaded Accumulator
Bladder type accumulator
Bladder type accumulator employs a bladder, as an elastic separator between the hydraulic fluid and the compressible gas, normally nitrogen.
|Bladder type Accumulator|
The bladder is fastened inside the steel shell by means of a vulcanized gas valve assembly. The bladder can be recharged, or replaced by removing it. The task of oil-valve assembly is to close the inlet opening when the bladder has expanded fully, thus preventing the bladder from being forced into the opening.
|Working of Bladder Type Accumulator|
The above figure shows the working of the bladder type accumulator. As shown in the figure, in a normal position, the bladder is fully expanded to the rated volume V0 and pressure of gas P0. As the accumulator is getting charged, the bladder goes on contracting due to compression of gas by hydraulic fluid. Accumulator gets charged until maximum working pressure P2 is reached and corresponding volume V2. Hence, the maximum charged volume of hydraulic fluid is equal to, ΔV=V1-V2.
Advantages of Bladder Type Accumulator
- Bladder provides positive sealing between the gas and the oil chamber.
- It is compact and light in weight.
- Since the bladder is a rubber element and has small inertia, it provides quick pressure response even to minute changes.
- They have very few functional parts and are less expensive.
Limitations of Bladder Type Accumulator
- The pressure exerted on the fluid is not constant and goes on reducing as the bladder goes on expanding.
- Comparatively smaller volumes are accommodated.
- The bladder is required to be replaced after a certain period of service.
- They cannot handle high-temperature fluids.
Applications of Bladder Type Accumulator
Diaphragm Type Accumulator
Diaphragm type accumulator uses a diaphragm as the elastic separator between the hydraulic fluid and the gas, normally nitrogen.
|Diaphragm type Accumulator|
A diaphragm is clamped between the walls of the pressure vessel. A shutoff button is fixed on the base of the diaphragm. This button serves to block the fluid inlet opening when the diaphragm is fully expanded, thus preventing the diaphragm from being forced into the opening.
The functioning of the diaphragm type accumulator is shown in the figure.
|Working of Diaphragm Type Accumulator|
In the normal position, the diaphragm is fully expanded to the rated volume V0 and the pressure of gas P0. As the accumulator starts getting charged, the diaphragm is pushed up, causing the compression of the gas.
Advantages of Diaphragm Type Accumulator
- The diaphragm provides positive sealing between the gas and the oil chamber.
- It is compact and lighter in weight as well there are no mechanically moving parts.
- It provides a quick response to even minute changes in pressure.
- Higher operating pressure than bladder type accumulator.
Limitations of Diaphragm Type Accumulator
- The pressure exerted on the fluid is not constant and goes on reducing as the diaphragm goes on expanding.
- Comparatively smaller volumes are accommodated.
- The diaphragm is required to be replaced after a certain period of time.
- It cannot handle high-temperature fluid.
Applications of Diaphragm Type Accumulator
Piston Type Gas Charged Accumulator
Advantages of Piston Type Gas Charged Accumulator
- It can handle high or low-temperature fluids.
- It can be mounted in any position, but vertical mounting is preferred.
- The piston provides a positive seal between gas and oil.
- Its working life is longer.
Limitations of Piston Type Gas Charged Accumulator
- Comparatively expensive to manufacture.
- The pressure is a function of compression of gas and varies with the volume of oil in the chamber.
- Comparatively slower response to pressure changes hence cannot be used as pressure pulsation damper.