hydraulics basics and components

Hydraulics ‒ Basics and Components

Introduction to Accumulator Technology

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V Introduction to Accumulator Technology1 Introduction �� 339

2 Product Overview Hydraulic Accumulators HYDAC �� 3412.1 Bladder accumulator �� 3412.2 Piston accumulator �� 3412.3 Diaphragm accumulator �� 3412.4 Metal Bellows Accumulator �� 3422.5 Hydraulic Dampers �� 3422.6 Special design accumulators �� 3422.7 Accumulator stations �� 3422.8 Accessories for accumulators �� 3432.8.1 Back�up of N2�bottles �� 3432.8.2 Charging and testing unit �� 3432.8.3 Safety and Shut�off Blocks �� 3432.8.4 Safety Equipment �� 3432.8.5 Fitting Elements for Hydraulic Accumulators �� 3432.8.6 ACCUSET SB330 �� 343

3 Designs of Hydropneumatic Accumulators and Accessories �� 3453.1 Bladder accumulators �� 3473.1.1 Special Design High�Flow Accumulators, Low Pressure �� 3493.2 Piston accumulator �� 3503.3 Diaphragm accumulators �� 3553.4 Metal bellows accumulators �� 3573.5 Weight Reduced Hydraulic Accumulators �� 3583.6 Hydraulic Dampers �� 3593.6.1 Pulsation dampers �� 3613.6.2 Suction stabilizers �� 3623.6.3 Silencers �� 3633.6.4 Shock Absorbers �� 364

4 Accumulator Stations �� 3674.1 RetrofittingofNitrogenBottlesinBladderAccumulators �� 3674.2 BladderAccumulatorswithRetrofittedNitrogenBottles �� 3684.3 RetrofittingofNitrogenBottlesinBladderAccumulators �� 3694.4 PistonAccumulatorswithRetrofittedNitrogenBottles �� 370

5 Accessories �� 3735.1 Universal Charging and Testing Unit FPU�1 �� 3735.2 Nitrogen Charging Unit �� 3745.3 Equipment and Safety Apparatus �� 3755.3.1 Safeguardingonfluidside �� 3765.3.1.1 Safety and shut�off block (SAF) �� 3765.3.1.2 DSV 10 �� 3785.3.1.3 Special designs with logic valves �� 3785.3.2 Safeguarding the gas side �� 3795.3.2.1 Fire protection �� 3795.3.2.2 Burst plates �� 3805.3.2.3 Gas safety valves �� 3805.3.2.4 Gas safety blocks �� 381

6 Application Cases for Hydraulic Accumulators �� 3836.1 Energy storage �� 3836.1.1 Energy Storage in Injection Molding Machines �� 3836.1.2 Energy storage and reduction of stroke time �� 3846.1.3 Energy storage for emergency function of hydraulic cylinders �� 3846.2 Volume compensation �� 3856.2.1 Volume compensation for leakage oil compensation �� 3856.3 Pulsation Damping �� 3866.3.1 Pulsation damping in a displacement pump �� 3866.4 Pressure surge damping �� 3876.4.1 Pressure surge damping in mobile units �� 3876.5 Separationoffluids �� 3886.6 Fluid based sound absorber �� 388

7 Application Examples for Hydraulic Accumulators �� 3897.1 Offshore Technology �� 3897.2 Systems engineering �� 3907.3 Mobile Technology�� 3907.4 Otherfields �� 390

8 Selection of hydropneumatic accumulators �� 3918.1 Selection Criteria �� 3918.2 Definitionofoperatingparameters �� 392

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8.3 DefinitionofTerms�� 3938.3.1 Isobaric �� 3938.3.2 Isochoric �� 3938.3.3 Isothermal �� 3938.3.4 Adiabatic �� 3938.3.5 Polytropic �� 3948.4 Calculation with Basic Physical Equations �� 3948.5 Selection of Gas Pre�charge Pressure �� 3988.6 Calculation on Deviation from Ideal Gas Behavior �� 3988.6 Calculation of Thermal Time Response �� 3998.8 Dimensioning Hydropneumatic Accumulators with ASP Software �� 400

9 Safety Regulations �� 401

List of figures − accumulator technology �� 402

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V Introduction to accumulator technology

1 IntroductionHydraulic accumulators are pressurized containers in which a certain useful volume is stored. If necessary, the stored fluidvolumecanbereturnedtothesystemwithoutfurthersupportiveenergy.Inordertostoreenergyinaccumulators,thefluidinanaccumulatorisweightorspringloadedorpressurizedbyagas(hydropneumatically).

Duetotheirsystemspecificadvantages,hydraulicaccumulatorsarethepreferredchoiceformiscellaneoustasksinhyd�raulic systems.

Application:•Energy storage•Emergency and safety functions•Leakage compensation•Volume compensation•Suctionflowstabilization•Dampingandcushioningofvibrations,fluctuations,pulsations(pulsationdamping)andshocksandsurges(shockab�sorption)aswellasnoiselevels(fluidsilencers)

•Separationoffluids•Weight equalization•Energy recovery

Note:All accumulators have to comply with the European Pressure Equipment Directive PED/DGRL 97/23/EC (see chapter 8)!

Fig. Hydraulic accumulator

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Notes:

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2 Product Overview Hydraulic Accumulators HYDAC2.1 Bladder accumulator

Type:Nominal volumes: Max. operating overpressure:

SB

0.5 � 450 liter Up to 1000 bar

Standard design:Nominal volumes: Max. operating overpressure: Special constructions:

0.5 � 200 liter 330 � 550 bar Stainless steel, composite construction

Low pressure design:Nominal volumes: Max. operating overpressure: 2.5 � 450 liter

Up to 40 barHigh pressure design:Nominal volumes: Max. operating overpressure:

1 � 54 liter 690 � 1000 bar

2.2 Piston accumulator

Type:Nominal volumes: Max. operating overpressure: Position indicators:

SK

Up to 3300 liter 1000 bar •Electricallimitswitch•Extendedpistonrod•Supersonicposition-measuringsystem•Cablecontrolmeasuringsystem•Magnetflapindicatingsystem•Pistonpositioningswitch

Standard design:Nominal volumes: Max. operating overpressure: Special constructions:

Up to 3300 liter 210 � 350 bar Stainless steel, composite construction, Up to 1000 bar as high pressure accumulator

Type series SK280:Nominal volumes: Max. operating overpressure:

0.16 � 6 liter 280 bar

2.3 Diaphragm accumulator


SBO

0.075 � 4 liter Up to 750 bar

Welded design:Nominal volumes: Max. operating overpressure:

0.075 � 4 liter 50 � 330 bar

Hreaded design:Nominal volumes: Max. operating overpressure:

0.1 � 4 liter 210 � 750 bar

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2.4 Metal Bellows Accumulator


SM

Up to 50 liter Up to 350 bar

2.5 Hydraulic Dampers

Type:

Nominal volumes: Max. operating overpressure:

•Pulsation dampers•Suctionflowstabilizers•Fluid silencers

0.075 � 450 liter 10 � 1000 bar

2.6 Special design accumulators

Weight-reduced bladder, piston and diaphragm accumulators. Weight can be saved through special production methods and the usage of alternative materials, such as aluminum. This is primarily used in mobile versions of the aggregates.

Spring loaded accumulators are equipped with a spring. In this case the energy is derived from that spring and not from gas.

Due to their composite structure (plastic/steel), the weight is reduced in compari�son to the standard steel accumulator design.

2.7 Accumulator stations

Accumulator stations are individually developed and constructed according to customer requirements. The following example shows an application with a pis�ton accumulator and nitrogen bottles.Piston accumulator station12x SK

12x SN

SS350K

750 l

3200 l

Dimensions47400 liter total gas volume11.94 m • 2.4 m • 10 m

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2.8 Accessories for accumulators

2.8.1 Back-up of N2-bottles

The nitrogen bottles are used as a back�up for bladder and piston accumulators. They increase the gas volume in the accumulator.

Nominal volume: 20 � 75 liter Effective gas volume: 17.5 � 75 liter

2.8.2 Charging and testing unit

Type: FPU Type: F+PTechnical Data: Technical Data:•FPU�1 universal charging and testing unit up to 400 bar p0 •Max. operating excess pressure: up to 400 bar•FPS6 for bladder accumulators up to 600 bar p0 •Nominal widths: DIN16/DN32•FPK600 for piston and diaphragm accumulator up to 600 bar p0 •Materials: Carbon steel, stainless steel•FPH800 for SB, SBO and SK up to 800 bar p0 •Optimized dimensions

2.8.3 Safety and Shut-off Blocks

Type: SAF/DSVNominal width: 10, 20, 32, 50 mmMax. excess operational pressure: Up to 400 bar (DSV to 350 bar)Pressure relief valve: Nominal width DN12

2.8.4 Safety Equipment

For the fluid side:•Direct acting safety valve, spring loaded•Response pressure: up to 370 bar•Design: DGRL 97/23/EC

For the gas side:•Direct acting gas safety valve GSV6 with CE marking, spring loaded•Temperature fuse with and without CE marking •Burst disk with CE marking•Gas safety block GSB450, an adaptor block to hold different components, e.g safety devices

2.8.5 Fitting Elements for Hydraulic Accumulators

Accumulatorsets,clampsandbracketsforoptimalfixing/mountingofhydraulicaccumulators.

2.8.6 ACCUSET SB330

Nominal volume: 1 � 50 literMax. operating excess pressure: up to 330 bar

Fig. Accessories for accumulators

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Notes:

345

3 Designs of Hydropneumatic Accumulators and AccessoriesWedistinguishhydraulicaccumulatorsaccordingtothedesignoftheirseparatorsbetweengasandfluids,aswellasthestorage medium (weight, spring or gas).All designs can store pressure energy.

In mechanical systems (weight and spring�loaded) energy is stored by the transformation of potential energy.

Fig. Designs of hydropneumatic accumulators

Accordingly, in gas-loaded accumulators, the inner energy of a gas is transformed. Hydropneumatic accumula-tors can be distinguished as follows:•Accumulators with separators•Accumulators without separators

Hydraulic accumulators can be also distinguished according to the separator between gas and fluid:•Bladder accumulator•Piston accumulator•Diaphragm accumulator•Metal bellows accumulators

The mode of operation of these accumulators is based on the compressibility of an inert gas, which is used for storing fluids. Usually nitrogen is used as the energy carrier.

Note:Due to the danger of explosion, only inert gases may be used for charging hydraulic accumulators! Hydropneumaticaccumulatorsessentiallyconsistofafluidandagassection,dividedbyagas-tightseparator.Thefluidsection is connected to the hydraulic circuit, meaning that when the pressure increases, the gas on the opposite side is compressed. If the pressure decreases, the compressed gas can expand again and the stored liquid is pushed back into the hydraulic circuit. Best suited as charging gas is nitrogen.

Weight�loaded Spring�loaded Air dome/air chamber

FLoadFSpring

FGas

FGas

Bladder accumulator

Diaphragm accumulator

Piston accumulator

Metal bellows accumulator

Withseparatorbetweengasandfluidside

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hydraulics basics and components

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