Hydraulics – Basics and Components

Hydraulics ‒ Basics and Components Introduction to Accumulator Technology

V Introduction to Accumulator Technology 1 Introduction �� 339 2 Product Overview Hydraulic Accumulators HYDAC �� 341 2.1 Bladder accumulator �� 341 2.2 Piston accumulator �� 341 2.3 Diaphragm accumulator �� 341 2.4 Metal Bellows Accumulator �� 342 2.5 Hydraulic Dampers �� 342 2.6 Special design accumulators �� 342 2.7 Accumulator stations �� 342 2.8 Accessories for accumulators �� 343 2.8.1 Back-up of N2-bottles �� 343 2.8.2 Charging and testing unit �� 343 2.8.3 Safety and Shut-off Blocks �� 343 2.8.4 Safety Equipment �� 343 2.8.5 Fitting Elements for Hydraulic Accumulators �� 343 2.8.6 ACCUSET SB330 �� 343

3 Designs of Hydropneumatic Accumulators and Accessories �� 345 3.1 Bladder accumulators �� 347 3.1.1 Special Design High-Flow Accumulators, Low Pressure �� 349 3.2 Piston accumulator �� 350 3.3 Diaphragm accumulators �� 355 3.4 Metal bellows accumulators �� 357 3.5 Weight Reduced Hydraulic Accumulators �� 358 3.6 Hydraulic Dampers �� 359 3.6.1 Pulsation dampers �� 361 3.6.2 Suction stabilizers �� 362 3.6.3 Silencers �� 363 3.6.4 Shock Absorbers �� 364

4 Accumulator Stations �� 367 4.1 Retrofitting of Nitrogen Bottles in Bladder Accumulators �� 367 4.2 Bladder Accumulators with Retrofitted Nitrogen Bottles �� 368 4.3 Retrofitting of Nitrogen Bottles in Bladder Accumulators �� 369 4.4 Piston Accumulators with Retrofitted Nitrogen Bottles �� 370

5 Accessories �� 373 5.1 Universal Charging and Testing Unit FPU-1 �� 373 5.2 Nitrogen Charging Unit �� 374 5.3 Equipment and Safety Apparatus �� 375 5.3.1 Safeguarding on fluid side �� 376 5.3.1.1 Safety and shut-off block (SAF) �� 376 5.3.1.2 DSV 10 �� 378 5.3.1.3 Special designs with logic valves �� 378 5.3.2 Safeguarding the gas side �� 379 5.3.2.1 Fire protection �� 379 5.3.2.2 Burst plates �� 380 5.3.2.3 Gas safety valves �� 380 5.3.2.4 Gas safety blocks �� 381

6 Application Cases for Hydraulic Accumulators �� 383 6.1 Energy storage �� 383 6.1.1 Energy Storage in Injection Molding Machines �� 383 6.1.2 Energy storage and reduction of stroke time �� 384 6.1.3 Energy storage for emergency function of hydraulic cylinders �� 384 6.2 Volume compensation �� 385 6.2.1 Volume compensation for leakage oil compensation �� 385 6.3 Pulsation Damping �� 386 6.3.1 Pulsation damping in a displacement pump �� 386 6.4 Pressure surge damping �� 387 6.4.1 Pressure surge damping in mobile units �� 387 6.5 Separation of fluids �� 388 6.6 Fluid based sound absorber �� 388

7 Application Examples for Hydraulic Accumulators �� 389 7.1 Offshore Technology �� 389 7.2 Systems engineering �� 390 7.3 Mobile Technology �� 390 7.4 Other fields �� 390

8 Selection of hydropneumatic accumulators �� 391 8.1 Selection Criteria �� 391 8.2 Definition of operating parameters �� 392 337 8.3 Definition of Terms �� 393 8.3.1 Isobaric �� 393 8.3.2 Isochoric �� 393 8.3.3 Isothermal �� 393 8.3.4 Adiabatic �� 393 8.3.5 Polytropic �� 394 8.4 Calculation with Basic Physical Equations �� 394 8.5 Selection of Gas Pre-charge Pressure �� 398 8.6 Calculation on Deviation from Ideal Gas Behavior �� 398 8.6 Calculation of Thermal Time Response �� 399 8.8 Dimensioning Hydropneumatic Accumulators with ASP Software �� 400

9 Safety Regulations �� 401 List of figures − accumulator technology------402

338 V Introduction to accumulator technology

1 Introduction Hydraulic accumulators are pressurized containers in which a certain useful volume is stored. If necessary, the stored fluid volume can be returned to the system without further supportive energy. In order to store energy in accumulators, the fluid in an accumulator is weight or spring loaded or pressurized by a gas (hydropneumatically). Due to their system specific advantages, hydraulic accumulators are the preferred choice for miscellaneous tasks in hyd� raulic systems.

Application: • Energy storage • Emergency and safety functions • Leakage compensation • Volume compensation • Suction flow stabilization • Damping and cushioning of vibrations, fluctuations, pulsations (pulsation damping) and shocks and surges (shock ab� sorption) as well as noise levels (fluid silencers) • Separation of fluids • 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

339 Notes:

340 2 Product Overview Hydraulic Accumulators HYDAC 2.1 Bladder accumulator

Type: SB Nominal volumes: 0.5 - 450 liter Max. operating overpressure: Up to 1000 bar

Standard design: Nominal volumes: 0.5 - 200 liter Max. operating overpressure: 330 - 550 bar Special constructions: Stainless steel, composite construction Low pressure design: Nominal volumes: Max. operating overpressure: 2.5 - 450 liter Up to 40 bar High pressure design: Nominal volumes: 1 - 54 liter Max. operating overpressure: 690 - 1000 bar

2.2 Piston accumulator

Type: SK Nominal volumes: Up to 3300 liter Max. operating overpressure: 1000 bar Position indicators: • Electrical limit switch • Extended piston rod • Supersonic position-measuring system • Cable control measuring system • Magnet flap indicating system • Piston positioning switch Standard design: Nominal volumes: Up to 3300 liter Max. operating overpressure: 210 - 350 bar Special constructions: Stainless steel, composite construction, Up to 1000 bar as high pressure accumulator Type series SK280: Nominal volumes: 0.16 - 6 liter Max. operating overpressure: 280 bar

2.3 Diaphragm accumulator

Type: SBO Nominal volumes: 0.075 - 4 liter Max. operating overpressure: Up to 750 bar Welded design: Nominal volumes: 0.075 - 4 liter Max. operating overpressure: 50 - 330 bar Hreaded design: Nominal volumes: 0.1 - 4 liter Max. operating overpressure: 210 - 750 bar

341 2.4 Metal Bellows Accumulator

Type: SM Nominal volumes: Up to 50 liter Max. operating overpressure: Up to 350 bar

2.5 Hydraulic Dampers

Type: • Pulsation dampers • Suction flow stabilizers • Fluid silencers Nominal volumes: 0.075 - 450 liter Max. operating overpressure: 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 station SS350K 12x SK 750 l

12x SN 3200 l 47400 liter total gas volume Dimensions 11.94 m • 2.4 m • 10 m

342 2.8 Accessories for accumulators

Fig. 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+P Technical 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/DSV Nominal width: 10, 20, 32, 50 mm Max. 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 Accumulator sets, clamps and brackets for optimal fixing/mounting of hydraulic accumulators.

2.8.6 ACCUSET SB330 Nominal volume: 1 - 50 liter Max. operating excess pressure: up to 330 bar

343 Notes:

344 3 Designs of Hydropneumatic Accumulators and Accessories We distinguish hydraulic accumulators according to the design of their separators between gas and fluids, as well as the storage 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.

FLoad FGas FSpring

FGas

Weight-loaded Spring-loaded Air dome/air chamber

With separator between gas and fluid side

Bladder Diaphragm Piston Metal bellows accumulator accumulator accumulator accumulator

Fig. Designs of hydropneumatic accumulators

Accordingly, in gas-loaded accumulators, the inner energy of a gas is transformed. Hydropneumatic accumulators 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! Hydropneumatic accumulators essentially consist of a fluid and a gas section, divided by a gas-tight separator. The fluid section 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.

345 Prospekt: Kühlsysteme DEF 5.700 Prospekt: Elektronik DEF 18.000 Accessories DEF 6.100 Compact Hydraulics DEF 5.300 Fluid Service DEF 7.929 Filters for Indust. Proces. DEF 7.700 Filtration Range DEF 7.000 Accumulators DEF 3.000 www.hydac.com Local expertise. Global presence. HYDAC Distributors Partners andService HYDAC Companies HYDAC Headquarters HYDAC Systems&ServicesGmbH Training Center E-Mail: [email protected] Internet: www.hydac.com +49 (0)6897/509-1014 Fax: +49 (0)6897/509-01 Phone: Germany 66280 Sulzbach/Saar Hirschbachstraße 2

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