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hydraulic accumulator is a pressure storage reservoir in which a
non compressible hydraulic fluid is retained under pressure from
an external source. Its main function is to store hydraulic energy
and is necessary, make the energy available again to the system.
A hydraulic accumulator is also referred to as the capacitance of
the system.
Types of Accumulators
The different types of accumulators include:
A. Dead weight type
The dead weight accumulator consists of a piston loaded with a dead
weight and moving within a cylinder that exerts pressure on the
hydraulic oil. The dead weight may be of some heavy material such
as iron, concrete block, pig or scrap iron etc. For minimum leakage
past the piston, it must be a precision fit in the accumulator tube
to ensure a long life.
- Advantages
Their advantage is that the pressure remains constant for the
full stroke. They supply large volumes of fluid under high pressure.
They can serve several hydraulic systems at a time and are most
often used in ill and central hydraulic systems.
- Disadvantages
The dead weight type accumulators, however, have some disadvantages
too. Being very bulky, the larger sizes are extremely expensive,
particularly those delivering high pressures and volumes.
B. Spring loaded type
Whether single-spring or multiple-spring type, the springs in this
accumulator, act against a hydraulic piston forcing the fluid into
the hydraulic system. A spring loaded accumulator consists of a
cylinder body, a movable piston and a spring. The spring applies
force to the piston. As fluid is pumped to it, the pressure in the
accumulator is determined by the compression rate of the spring.
- Advantages
These accumulators are usually smaller less expensive than the
dead weight type and mounting is easy. They are built directly
into the power unit.
- Disadvantages
They supply a small volume of oil at low pressure. The pressure
does not remain constant, the accumulator pressure reaching its
peak as the spring compresses and drops to a minimum as the springs
approach free length. It has to be taken care of that the leakage
oil is vented from the spring chamber.
C. Hydro-pneumatic type
The hydro-pneumatic accumulators are the most commonly used accumulators
and apply force to the liquid by using a compressed gas that acts
as the spring. It uses only dry nitrogen as there is a danger of
exploding an air-oil vapor, in the case of compressed air.
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