Types of Hydraulic Accumulators | Their Working, Applications

The purpose of an accumulator is to store hydraulic energy in the form of pressurized fluid, provided by the pump, and later provide it to the system whenever needed. Because of their ability to store excess energy and release it when needed, accumulators are useful tools in developing an efficient hydraulic system.

Accumulators are found in numerous applications, they are used in conjugation with the hydraulic system on large hydraulic presses, construction equipment, farm machinery, power brakes, automotive suspensions, hatch covers on ships, landing gear mechanism on airplanes, etc.

Accumulators are generally classified by means of the use of energy storage. There are basically three types of accumulators,

Gas loaded accumulators are further divided as the non-separator type and separator type.

Separator type gas loaded accumulators consist of

Types of Hydraulic Accumulators

Let us discuss these types of accumulators in brief.

A weight loaded accumulator is shown in the figure.

Weight Loaded Accumulator

Weight loaded accumulator consists of a ram loaded with dead weight. The mass of dead weight may be concrete steel or other heavy material. The piston rod is much bigger in size to avoid buckling failure due to heavy load. The accumulator pressure is given by,

Where,

d = Diameter of piston

W = Deadweight

w = Piston and Piston rod weight

And volumetric Capacity of weight loaded accumulator is given by,

V_acc = π/4 x (d²) x L

Where,

L = Piston stroke length

Due to their size and bulk, their applications are limited to stationary equipment such as heavy-duty presses, where large volumes are required.

A spring-loaded accumulator is shown in the figure below.

Spring-loaded Accumulator

Spring-loaded accumulator consists of a cylinder containing a spring-loaded piston, with fluid entering on another side of the cylinder. The fluid is stored under pressure by the spring force. As the spring is compressed completely, the accumulator pressure reaches its peak and as the spring approaches its free length, the accumulator pressure drops to its minimum. The design is mostly multi-spring, to reduce the size of the accumulator for the same pressure.

Spring-loaded accumulators are used where space limitation is the primary criterion and considerably smaller volumes are required. For example, automotive and mobile hydraulic applications.

A gas-charged accumulator pressurizes the fluid by the pressure of the gas. Gas loaded accumulators are also called 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.

Non-separator type gas loaded accumulator is used in applications where the hydraulic fluid used in the system has high sir separate-ability, and the slight missing of gas in fluid doesn’t create any functional problems.

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 using 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 P_0. 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-V_2.

Read More: Construction, Working, And Applications of Hydraulic Press

Later, whenever the system needs the fluid it is discharged by the expansion of the bladder.

• The 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 a 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

Due to the quick-responding nature, the bladder type accumulator is widely used in the wheel suspension system of automotive vehicles. Further, it is found applicable where smaller volumes at comparatively higher pressure are required.

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.

When the maximum working pressure P₂ is reached, the accumulator is said to be fully charged. This volume is equal to, ΔV=V₁-V₂

Afterward, whenever the system needs the fluid, it is discharged due to the expansion of the gas contained part of the vessel.

• 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.
• It cannot handle high-temperature fluid.

Applications of Diaphragm Type Accumulator

Due to its quick-responding nature, it is widely used in the wheel suspension system of automotive vehicles. Further, it is found applicable where smaller volumes at comparatively higher pressure are required.

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 the 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.

Applications of Piston Type Gas Charged Accumulator

Due to its expensive nature, their application is limited to high-temperature systems with smaller volume requirements.

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