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A bladder accumulator consists of a seamless cylindrical pressure vessel (shell), internal elastomeric bladder, poppet valve, fluid (oil) port, charging valve, and clamps and brackets. A schematic diagram of a bladder accumulator is shown in the figure below and the basic constructional features and specification parameters are highlighted in the subsequent sections.
Figure | A bladder accumulator
Shell, Bladder Accumulator
The shell is made of carbon steel, stainless steel, or low-temperature steel. For use with a chemically aggressive fluid, the interior of the carbon steel shell can optionally be provided with corrosion protection. Alternatively, stainless steel can be used for the accumulator parts that are liable to be exposed to a corrosive environment.
A full range of bladders is developed from the most advanced elastomers capable of meeting a wide range of temperatures from -45ºC [-50ºF] to +150ºC [300ºF]. They must also be compatible with a wide variety of fluids.
Buna-N is the standard material used for the bladder and is suitable for most fluid power applications. Other materials, such as low-temperature Buna-N (ECO), Viton (Fluorine rubber, FKM), Butyl, and Hydrin, are also used as bladder materials.
Poppet Valve, Bladder Accumulator
The fluid chamber in a bladder accumulator is provided with a spring-loaded poppet valve. This valve prevents the extrusion of the bladder into the downstream tubing, in case the bladder over-expands.
Fluid Port, Bladder Accumulator
The fluid chamber includes standard ports with threads conforming to ISO (metric), DIN, ANSI (NPT), etc., or special bolt-on flanges conforming to DIN, ANSI, SAE, etc., for making a direct connection to the associated hydraulic system.
Bladder Accumulator Models
Bladder accumulators are designed as bottom-repairable and top-repairable models.
Clamps and Brackets
Clamps and brackets can be used to mount accumulators for their proper support and isolation from system vibrations.
The gas chamber is pre-charged with nitrogen gas to a certain pressure level using a nitrogen source and a charging kit.
Bladder accumulators can be installed vertically, horizontally, or at any angle depending upon the application requirements. For example, the vertical position of the accumulator is preferable for energy storage applications.
Advantages and Limitation
Bladder accumulators are fast-acting and do not exhibit hysteresis. The main limitation of the bladder accumulators is that they are larger than other types of comparable accumulators.
Accumulators can be dangerous to personnel and property if they discharge the stored pressure inadvertently. Therefore, it is necessary to isolate the accumulators from the associated systems and discharge the pressures from the accumulators, during periods of maintenance. Typically, safety devices must be incorporated in an accumulator to provide a shut-off facility and pressure-limiting and pressure relief features. A safety-and-shut-off block consists of a shut-off valve, manual bleed valve, pressure relief valve, optional 2-way solenoid-operated bleed valve and pressure gauge.
Specification Parameters, Accumulator
- Nominal volume
- Gas compression ratio
- Flow rate
- Effective gas volume
- Maximum working pressure
- Shell material
- Bladder material
- Corrosion protection
- Accumulator Model
- Fluid port material
- Fluid port size
- Fluid port connection
- Gas port size
- Gas port connection
- Gas charge kit
- Mounting support
- Operating temp
- Country of destination
- Standards for compliance
- Shell certification
Specification Parameters, Safety and Shut-off Block
- Size (eg. DN08, NG 10 etc)
- Maximum operating pressure (eg. 350 bar / 5000 psi)
- Shut off valve, poppet type
- Bleed valve, poppet type (Manual, Manual + Solenoid)
- Pressure relief valve Rating (eg. 350 bar / 5000 psi)
- Seal (eg. Nitrile)
- Type of connection (eg. sub-plate connection)
- Port sizes (G½ to G 1½)
- Accumulator-side connection type (eg. Threaded)
- Pressure port and gauge port connection types
- Tank port connection type
Fluid Power Educational Series Books
More details about Accumulators can be accessed from the following low-cost books by the author.
Hydraulic Accumulators and Circuits in the SI Units
Accumulators in Hydraulic Systems in the English Units
The book brings out the essential technical information related to hydraulic accumulators extracted, especially from the materials available from the manufacturer’s domain. The book explains the functions, classification, constructional details, and comparison of many types of accumulators including piston, diaphragm, and bladder types. Further, the book presents the topics on pre-charging, safety requirements, and applications of accumulators, in sufficient detail. A chapter gives basic circuits of accumulators. Another chapter presents the topic of the sizing of accumulators with many numerical examples. The topics of maintenance and specifications of accumulators are given at the end of the book.
Many other fluid power topics are given in other simple-to-understand books in paperback and Kindle eBook formats under the fluid power educational series by the same author. Also, please see the details at https://jojibooks.com