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.
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.
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.
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.
These accumulators are usually smaller less expensive than the dead
weight type and mounting is easy. They are built directly into the power
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.
The different types of hydro-pneumatic accumulators used are:
1. Non-separator type, but not used due to possibility of foaming
It consists of a cylinder with hydraulic fluid and the charging gas
with no separation between them. They are generally used on die casting
machines or other similar places. They are always to be mounted
It consists of a cylinder body and a movable piston. The gas that
occupies the volume above the piston is compressed as the cylinder body
is charged with liquid.
It consists of two metal hemispheres which are separated by flexible,
synthetic rubber diaphragm. The storing action is effected by the
compression of the volume of nitrogen enclosed in the diaphragm.
It consists of a synthetic polymer rubber bladder like chloroprene,
nitrile, etc. inside a metal (steel) shell. The bladder is filled with
compressed gas. It responds quickly for receiving or expelling flow of
oil. There is always a possibility of bladder failure that needs to be
taken into consideration.
The hydraulic accumulators are applicable for hydraulic shock
suppression are suitable for leakage compensation. The accumulators are
the source of power during power failures. They aptly hold high pressure
for long periods without keeping the pump running.
They have wide applicability in large hydraulic presses, diesel engine
starters, hydraulically operated hospital beds, farm machinery, landing
gear mechanism on airplanes, hatch cover in ships, lifts, trucks, etc.
Guidelines for Safety
1. In order to avoid the danger of explosion, the air or oxygen should
not be used or allowed to enter the system. 2. Repair or connection of
pressure gauge should be done after the release of fluid pressure. 3.
The gas precharge pressure should lie below the minimum operating
pressure. 4. Bladders should be hanging by the gas valve and blown up
with air to their full length and not stored folded. 5. The accumulators
should be always fitted with robust bracket and a pressure relief valve.
6. There should be a non-return valve fitted with an accumulator to
prevent oil from flowing back to the pump.