Introduction and Types of Hydraulic Accumulator.

1. Subject :Fluid Power Engineering (2151903)
Topic: Hydraulic Accumulator
GANDHINAGAR INSTITUTE
OF TECHNOLOGY(012)

2. Content
 Introduction
 Types of HydraulicAccumulator
 Functions of Accumulator
 Accumulator Design Consideration
 Application
 Conclusion

3. 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.

4. 1. Tower typeaccumulator
2. Raised weightaccumulator
3. Compressed-gasaccumulator
a) Bladder typeaccumulator
b) Diaphragm typeaccumulator
c) Piston typeaccumulator
d) Metal bellow typeaccumulator
4. Spring accumulator
Types of Hydraulic Accumulator

5. 1. TOWER TYPE ACCUMULATOR
 The first accumulators for
Armstrong’s hydraulic dock
machinery were simple raised
water tower.
 It uses hydraulic head
 It delivers constant pressure to
the output
LONDON TOWER BRIDGE

6. 2. RAISED 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
pistonand thereby energizes the
fluid in thecylinder.

7. ADVANTGES :
 Used to meet heavy industrial
requirements.
 Extremely high capacity atlow cost.
 Rugged and durableconstruction.
LIMITATIONS :
 Extremely bulky and heavy.
 Problem in sealing.
 In contrast to compressed gas accumulator,
this type delivers a nearly constant pressure,
regardless of thevolume of fluid in the
cylinder, until it isempty
Hydraulicengine
house, Bristol Harbor.

8. 3. COMPRESSED GAS ACCUMULATOR
 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 onfluid.
 Oxygen is not used because oxygen and oil can form an
explosive mixture when combined underpressure
 As the volume of the compressed gas changes the
pressure of the gas, and pressure of the fluid, changes
inversely.

9. 4. Spring type 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 representszero
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.

10.  It acts according to Hook’s law, magnitude of
theforce exerted by the spring is linearly
proportional to its extension.
Spring loaded accumulator

11. 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 andvalves.
 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.

12.  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
Accumulator
P-port
Shut-off valve
Discharge valve,electric
(optional)
Manifold Block
Pressure-
relief
valve
Gauge
port
Discharge,
manual
Hydraulic
Symbol
Adapter
fitting, Flange

13. 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

14. 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 operationalcircuit.
 Clamping devices to hold the jaw vices and fixtures
 Standby power supplycircuits.
 Surge reductioncircuits
 Agricultural Machinery & Equipment
 Forestry Equipment
 Oil Field & Offshore
 Machine Tools and Off- RoadEquipment
 Mining Machinery & Equipment
 Mobile & Construction Equipment
 Suspension in vehicles

15. 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, reduceleakage
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.

16.  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 industrialmachinery
using accumulators.