2. INTRODUCTION
A Hydraulic Accumulator is energy storage device.
It is pressure storage reservoir in which a non-
compressible hydraulic fluid is held under pressure by an
external source.
The external source used can be a spring, a raised weight,
or a compressed gas.
The main reasons that an accumulator is used in a
hydraulic system, is that the pump doesn’t need to be so
large to cope with extremes of demand and supply circuit
can respond quickly to any temporary demand and to
smooth pulsation.
3. 1. Dead weight accumulator
2. Spring loaded accumulator
3. Compressed-gas accumulator
A. Non separator type accumulator
B. Separator type accumulator
a) Bladder type accumulator
b) Diaphragm type accumulator
c) Piston type accumulator
d) Metal bellow type accumulator
TYPES OF HYDRAULIC ACCULUMATOR
4. 01. Weight-loaded or gravity accumulator:
Schematic diagram of weight loaded accumulator is shown in Figure.
It is a vertically mounted cylinder with a large weight. When the
hydraulic fluid is pumped into it, the weight is raised. The weight
applies a force on the piston that generates a pressure on the fluid
side of piston. The advantage of this type of accumulator over other
types is that it applies a constant pressure on the fluid throughout its
range of motion. The main disadvantage is its extremely large size
and heavy weight. This makes it unsuitable for mobile application.
6. DEAD WEIGHT ACCUMULATOR
A raised weight accumulator consists of
a vertical cylinder containing fluid to the
hydraulic line.
The cylinder is closed by a piston on
which a series of weights are placed that
exert a downward force on the piston
and thereby energizes the fluid in the
cylinder.
Gravity acts on the weight to pressurize
the hydraulic system fluid, thus storing
energy.
7. ADVANTGES :
Used to meet heavy industrial
requirements.
Extremely high capacity at low cost.
Rugged and durable construction.
LIMITATIONS :
Extremely bulky and heavy.
Problem in sealing.
In contrast to compressed gas
accumulator, this type delivers a nearly
constant pressure, regardless of the
volume of fluid in the cylinder, until it is
empty Hydraulic engine
house, Bristol Harbor.
8. 2. Spring Loaded Accumulator
It uses the energy stored in springs to create a constant force on
the liquid contained in an adjacent ram assembly.
The load characteristics of a spring are such that the energy
storage depends on the force required to compress s spring.
The free (uncompressed) length of a spring represents zero energy
storage.
As a spring is compressed to the maximum installed length, high
pressure value of the liquid in a ram assembly is established.
As liquid under pressure enters the ram cylinder, causing a spring
to compress, the pressure on the liquid will rise because of the
increased loading required to compress the spring.
It acts according to Hook’s law, magnitude of the force exerted by
the spring is linearly proportional to its extension.
10. There are two types of gas-loaded accumulators:
Non-separator-type accumulator: Here the oil and gas are not
separated. Hence, they are always placed vertically.
Fluid
GAS
Charging valve
Fluid from
pump
Fluid to system
Non-separator type accumulator
11. 3. COMPRESSED GAS ACCUMULATOR
Separator-type accumulator: Here the oil and gas are separated
by an element. Based on the type of element used to separate the
oil and gas, they are classified.
It is widely used accumulator in present scenario.
It is popularly known as “hydro-pneumatic accumulator”. It
apply force to the liquid by using a compressed gas that acts as
the spring.
It uses inert gas (nitrogen) under pressure that provides the
compressive force on fluid.
Oxygen is not used because oxygen and oil can form an
explosive mixture when combined under pressure
As the volume of the compressed gas changes the pressure of the
gas, and pressure of the fluid, changes inversely.
12. a) BLADDER TYPE ACCUMULATOR
A bladder accumulator consists of seamless high-pressure
cylinder with an internal elastomeric bladder with pressurized
nitrogen on it and hydraulic fluid on the other(external) side.
The accumulator is charged with nitrogen through a valve
installed on the top. The accumulator will be pre-charged to
nominal pressure when the pumps are not operating.
The maximum flow rate of the accumulator is controlled by the
opening orifice and the pressure difference across the opening.
Bladder material widely used are epichlorohydric rubber(ECO)
and Acrylonitrile butadiene rubber (NBR).
14. ADVANTAGES :
Fast acting
Not susceptible to contamination
Consists behavior under similar condition
LIMITATIONS :
Compressed ratio is limited,
approximately 4:1
Bladder failure.
15. b) DIAPHRAGM TYPE ACCUMULATOR
A similar to bladder type, expect an elastomeric diaphragm is
used in place of a bag.
This would typically reduce the usable volume of the
accumulator, so the diaphragm accumulator may not have volume
capacity of a bladder accumulator.
Diaphragm accumulator may be spherical or cylindrical.
The main difference with bladder accumulator is an increased
maximum compression ratio of approximately 8:1
It is low weight, compact design and good for shock applications
(good response characteristics)
18. c) PISTON TYPE ACCUMULATOR
This accumulator consists of a cylinder assembly, a piston
assembly, and two end-cap assemblies.
An accumulator contains a free-floating piston with liquid on
one side of the piston and pre-charged air or nitrogen on the
other side.
An increase of liquid volume decreases the gas volume and
increases gas pressure, which provides a work potential when
the liquid is allowed to dis-charged.
19. PISTON TYPE ACCUMULATOR
ADVANTAGES :
High compression ratio up to 10:1
Higher flow rate than bladder type.
LIMITATIONS :
They are more susceptible to fluid contamination
Lower response time than the bladder and diaphragm
20. d) METAL BELLOW ACCUMULATOR
The metal bellows accumulator is
similar to bladder type, expect the elastic
is replaced by a hermitically sealed
welded metal bellows.
Fluid may be internal or external to the
bellows.
It is used when a fast response time is not
critical, yet reliability is important.
Metal bellow types are pre-charged by
supplier and then permanently sealed
leading to a maintenance free
accumulator.
Internal
21. METAL BELLOW ACCUMULATOR
ADVANTGES :
Metal bellow type include exceptionally low
spring rate, allowing the gas charge to do all
the work with little change in pressure from
full to empty, and long stroke relative solid
height, which gives maximum storage volume
for a given container size.
It provides exceptionally high level
accumulator performance.
It can be produced with broad spectrum of
alloys resulting broad range of fluid
compatibility.
LIMITATIONS :
Response time is more
High cost
External
External
23. FUNCTIONS : Where are accumulators used?
Accumulators can be applied creatively in any number of situations, including:
Emergency and safety: An accumulator which is kept constantly under
pressure is valuable in the event of an electrical power failure as it can provide
flow and pressure to perform an additional function or complete a machine
cycle.
Shock or pulsation dampening: An accumulator can be used to cushion the
pressure spike from sudden valve closure, the pulsation from pumps or the load
reaction from sudden movement of parts connected to hydraulic cylinders.
Leakage compensation: An accumulator can be used to maintain pressure
and make-up for lost fluid due to internal leakage of system components
including cylinders and valves.
Thermal expansion: An accumulator can absorb the pressure differences
caused by temperature variations in a closed hydraulic system.
Noise reduction: An accumulator is effective at reducing hydraulic system
noise caused by relief valves, pump pulsations, system shock and other circuit
generated noises.
24. Energy conservation: An accumulator can be used to supplement a pump
during peak demand thereby reducing the size of the pump and motor
required. The accumulator is charged during low demand portions of the pump
cycle time and then discharges during the high demand portions of the system.
Improved response times: An accumulator (bladder type) has virtually
instantaneous response time that can provide fluid very quickly to fast-acting
valves such as servos and proportional to improve their effectiveness
Discharge valve, electric
(optional)
Accumulator
P-port
Gauge
portShut-off valve
Manifold Block
Pressure-
relief
valve
Discharge,
manual
Hydraulic
Symbol
Adapter fitting,
Flange
25. ACCUMULATOR DESIGN CONSIDERATION :
(What must I know to size and select an accumulator?)
Accumulator type
Accumulator volume
Nominal hydraulic system pressure
Minimum and Maximum hydraulic system pressure
Pre-charge pressure
Required flow rate
Output volume capacity
Recharge time
Response time
Fluid type
26. measuring
jar
4/3 directional
valve with solenoid
actuation
Cylinder assembly
Accumulator
Hydraulic Pumppower unit
Check
valve
Hydraulic –accumulator circuit
PRV
27. APPLICATIONS
Accumulators are devices used to store fluid power to do the following:
Dampen pulsations and shocks of a periodic nature
Increase the speed of the operational circuit.
Clamping devices to hold the jaw vices and fixtures
Standby power supply circuits.
Surge reduction circuits
Agricultural Machinery & Equipment
Forestry Equipment
Oil Field & Offshore
Machine Tools and Off- Road Equipment
Mining Machinery & Equipment
Mobile & Construction Equipment
Suspension in vehicles
31. CONCLUSION
So what are the benefits of using accumulators?
Lower installed system costs, accumulator assisted
hydraulics can reduce the size of the pump and electric
motor which results in a smaller amount of oil used, a
smaller reservoir and reduced equipment costs.
Less leakage and maintenance costs, the ability to reduce
system shocks will prolong component life, reduce leakage
from pipe joints and minimize hydraulic system
maintenance costs.
Improved performance, low inertia bladder accumulators
can provide instantaneous response time to meet peak flow
requirements. They can also help to achieve constant
pressure in systems using variable displacement pumps for
improved productivity and quality.
32. Reduced noise levels, reduced pump and motor size
couple with system shock absorption overall machine
sound levels and results in higher operator
productivity.
Flexible design approaches. A wide range of
accumulator types and sizes, including accessory
items, provides a versatile and easy to apply design
approach.
Reduced energy costs, cost savings of up to 33% are
achievable in high performance industrial machinery
using accumulators.
