1. 1. Chandan Nagaraja1RV08ME021R.V.College of Engineering,Bengaluru
2. 2. OVERVIEW Introduction History Types of Hydraulic Accumulator Functions of Accumulator Accumulator design consideration Application Conclusion
3. 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. 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. 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. 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. 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. 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. 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. 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. 11. Bladder Accumulator(Various stages of operation)
12. 12. ADVANTAGES : Fast acting Not susceptible to contamination Consists behavior under similar conditionLIMITATIONS : Compressed ratio islimited,approximately 4:1 Bladder failure.
13. 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. 14. DIAPHRAGM TYPE ACCUMULATOR
15. 15. DIAPHRAGM TYPE ACCUMULATOR
16. 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. 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. 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. 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. 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. 21. Spring loaded accumulator It acts according to Hooks law, magnitude of the forceexerted by the spring is linearly proportional to itsextension.
22. 22. HYDARULIC SYMBOLS
23. 23. HYDARULIC SYMBOLS
24. 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. 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. 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. 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. 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. 29.
30. 30. Hydraulic accumulator circuitAccumulator Cylinder assembly4/3 directionalvalve with solenoidactuationPRVCheckmeasuringvalvejarpower unit Hydraulic Pump
31. 31. Electrical circuit
32. 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. 33. Energy Storage in an Injection Molding Machine Accumulator safety blockHydro electric forPressure Switch diaphragm- type
34. 34. Leakage Oil Compensation circuit & Shortening Time circuitof Stroke Time
35. 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. 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.