1. Chandan Nagaraja1RV08ME021R.V.College of
Engineering,Bengaluru
2. OVERVIEW Introduction History Types of Hydraulic Accumulator
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
anexternal source. The external source used can be a spring, a
raisedweight, or a compressed gas. The main reasons that an
accumulator is used in ahydraulic system, is that the pump doesnt
need to be solarge to cope with extremes of demand and supply
circuitcan respond quickly to any temporary demand and tosmooth
pulsation.
4. HISTORY First Hydraulic accumulator was madeby William
Armstrong in 1846 built acrane powered by water of town mainsat
Newcastle, United Kingdom. Later 1852 ,Armstrong used GrimsbyDock
Tower for the constant pressurefor cranes, lock gates and sluices.
Grimsby Dock Tower is hydraulicaccumulator is used for the purpose
ofcontaining a 30,000UK gallon (136 m3)hydraulic wrought iron
reservoir at aheight of 300feet (91 m) to providepower for lock
gates and cranes ofGrimsby Dock.
5. TYPES OF HYDRAULICACCULUMATOR1. Tower type accumulator2.
Raised weight accumulator3. Compressed-gas accumulatora) Bladder
type accumulatorb) Diaphragm type accumulatorc) Piston type
accumulatord) Metal bellow type accumulator4. Spring
accumulator
6. 1. TOWER TYPE ACCUMULATOR The first accumulators
forArmstrongs hydraulic dockmachinery were simple raised
watertower. It uses hydraulic head It delivers constant pressure to
theoutput LONDON TOWER BRIDGE
7. 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 piston and
thereby energizes the fluid in the cylinder. Gravity acts on the
weight to pressurize the hydraulic system fluid, thus storing
energy.
8. ADVANTGES : Used to meet heavy industrialrequirements.
Extremely high capacity at low cost. Rugged and durable
construction.LIMITATIONS : Extremely bulky and heavy. Problem in
sealing. In contrast to compressed gasHydraulic engineaccumulator,
this type delivers a nearlyhouse, Bristol Harbor.constant pressure,
regardless of the volumeof fluid in the cylinder, until it is
empty
9. 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 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.
10. a) BLADDER TYPE ACCUMULATOR A bladder accumulator consists
of seamless high-pressure cylinder with an internal elastomeric
bladderwith pressurized nitrogen on it and hydraulic fluid onthe
other(external) side. The accumulator is charged with nitrogen
through avalve installed on the top. The accumulator will
bepre-charged to nominal pressure when the pumps arenot operating.
The maximum flow rate of the accumulator is controlledby the
opening orifice and the pressure difference acrossthe opening.
Bladder material widely used are epichlorohydricrubber(ECO) and
Acrylonitrile butadiene rubber (NBR).
11. Bladder Accumulator(Various stages of operation)
12. ADVANTAGES : Fast acting Not susceptible to contamination
Consists behavior under similar conditionLIMITATIONS : Compressed
ratio islimited,approximately 4:1 Bladder failure.
13. 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)
14. DIAPHRAGM TYPE ACCUMULATOR
15. DIAPHRAGM TYPE ACCUMULATOR
16. 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.
17. PISTON TYPE ACCUMULATORADVANTAGES : 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
18. 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. Internal 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.
19. METAL BELLOW ACCUMULATORADVANTGES : Metal bellow type
include exceptionally lowspring rate, allowing the gas charge to do
all thework with little change in pressure from full toempty, and
long stroke relative solidheight, which gives maximum storage
volumefor a given container size. It provides exceptionally high
level accumulatorperformance. It can be produced with broad
spectrum ofalloys resulting broad range of
fluidcompatibility.LIMITATIONS : Response time is more High cost
External External
20. 4. Spring type accumulator It uses the energy stored in
springs to create a constant forceon the liquid contained in an
adjacent ram assembly. The load characteristics of a spring are
such that the energystorage depends on the force required to
compress s spring. The free (uncompressed) length of a spring
represents zeroenergy storage. As a spring is compressed to the
maximum installedlength, high pressure value of the liquid in a ram
assembly isestablished. As liquid under pressure enters the ram
cylinder, causing aspring to compress, the pressure on the liquid
will risebecause of the increased loading required to compress
thespring.
21. Spring loaded accumulator It acts according to Hooks law,
magnitude of the forceexerted by the spring is linearly
proportional to itsextension.
22. HYDARULIC SYMBOLS
23. HYDARULIC SYMBOLS
24. 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
underpressure is valuable in the event of an electrical power
failure as it can provideflow and pressure to perform an additional
function or complete a machinecycle. Shock or pulsation dampening:
An accumulator can be used to cushion thepressure spike from sudden
valve closure, the pulsation from pumps or the loadreaction from
sudden movement of parts connected to hydraulic cylinders. Leakage
compensation: An accumulator can be used to maintain pressureand
make-up for lost fluid due to internal leakage of system
componentsincluding cylinders and valves. Thermal expansion: An
accumulator can absorb the pressure differencescaused by
temperature variations in a closed hydraulic system. Noise
reduction: An accumulator is effective at reducing hydraulic
systemnoise caused by relief valves, pump pulsations, system shock
and other circuitgenerated noises.
25. 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
AccumulatorAdapter Discharge,fitting, Flange
manualPressure-Hydraulic Discharge valve,
electricreliefSymbol(optional)valveManifold BlockGauge P-port
portShut-off valve
26. 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
27. CALACULATIONSPressures :For the calculation of an
accumulator, the following pressures are of decisive
significance:p0= gas charge pressure at room temperatureand drained
fluid chamberp0 (t )= gas charge pressure at operating
temperaturep0 (tmax) = gas charge pressure at max. operating
temperaturep1 = minimum operating pressurep2 = maximum operating
pressurepm = medium operating pressureV0 = nominal capacity of the
accumulatorTo achieve the best possible utilization of the
accumulator capacity and a long service life, it isrecommended that
the following values be adhered to: p0 (tmax) 0.9* p1 (1)The
highest hydraulic pressure should not exceed the quadruple of the
pre-charge pressure;otherwise, the elasticity of the bladder is
overstressed and excessive variations in the compressionresult in
strong heating up of the gas:p2 4 * p0 (2)
28. Conta) In the case of isothermal changes of state of gases,
that is, when the gas buffer changesso slowly that enough time is
available for a complete heat exchange between the nitrogen and
itssurroundings and the temperature therefore remains constant, the
following is valid: p0 V0 = p1 V1 = p2 V2(3.1)b) In the case of an
adiabatic change of state, that is, with a rapid change of the gas
buffer, inwhich the temperature of the nitrogen changes as well,
the following is valid: p0 V0^ = p1 V1^ = p2 V2^(3.2) = ratio of
the specific heat of gases (adiabatic exponent) for nitrogen =
1.4In practice, changes in state rather follow adiabatic laws.
Charging is often isothermal, dischargingadiabatic.Oil volume :
Pressures p0 p2 determine gas volumes V0 V2. Here, V0 is also the
nominalcapacity of the accumulator. The available oil volume V
corresponds to the difference between gasvolumes V1 and V2: dV V1
V2 (4)
29.
30. Hydraulic accumulator circuitAccumulator Cylinder
assembly4/3 directionalvalve with
solenoidactuationPRVCheckmeasuringvalvejarpower unit Hydraulic
Pump
31. Electrical circuit
32. APPLICATIONSAccumulators 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
33. Energy Storage in an Injection Molding Machine Accumulator
safety blockHydro electric forPressure Switch diaphragm- type
34. Leakage Oil Compensation circuit & Shortening Time
circuitof Stroke Time
35. CONCLUSION So what are the benefits of using accumulators?
Lower installed system costs, accumulator assistedhydraulics can
reduce the size of the pump and electricmotor which results in a
smaller amount of oil used, asmaller reservoir and reduced
equipment costs. Less leakage and maintenance costs, the ability to
reducesystem shocks will prolong component life, reduce leakagefrom
pipe joints and minimize hydraulic systemmaintenance costs.
Improved performance, low inertia bladder accumulatorscan provide
instantaneous response time to meet peak flowrequirements. They can
also help to achieve constantpressure in systems using variable
displacement pumps forimproved productivity and quality.
36. 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.