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Accumulators
 The bladder accumulator consists of a fluid
section and a gas section, with the bladder acting as a gas-proof
screen. The fluid around the bladder is connected with the hydraulic
circuit, so that the bladder accumulator draws in fluid when the
pressure increases thus compressing the gas. When the pressure drops,
the compressed gas expands and forces the stored fluid into the circuit.
Construction
HYDAC
bladder accumulators consist of a welded or forged pressure vessel
(shell), a bladder and ports for gas and fluid inlet. The gas and fluid
sides are separated by the bladder.
Bladder Materials
Not all
fluids are compatible with every elastomer at all temperatures.
Therefore, HYDAC offers the following choice of elastomers:
• NBR (Standard Nitrile)
• LT-NBR (Low Temp. Nitrile)
• ECO (Epichlorohydrin)
• IIR (Butyl)
• FPM (Fluorelastomer)
• Others (available upon request)
To determine which material is appropriate ... Always Refer To Fluid Manufacturer’s Recommendation.
Corrosion Protection
For
use with certain aggressive or corrosive fluids, or in a corrosive
environment, HYDAC offers protective coatings and corrosive resistant
materials (i.e. stainless steel) for the accumulator parts that come in
contact with the fluid, or are exposed to the hostile environment.
Mounting Position
HYDAC
bladder accumulators can be installed vertically, at any angle, or
horizontally depending upon the application. When installing vertically
or at an angle, the fluid port must be at the bottom. On certain
applications listed below, specific positions are preferable:
• Energy Storage: vertical
• Pulsation Damping: any position from vertical to horizontal
• Maintaining Constant Pressure: any position from vertical to horizontal
• Volume Compensation: any position from vertical to horizontal
System Mounting
HYDAC
bladder accumulators are designed to be screwed directly onto the
system. We also recommend the use of our mounting components to
minimize risk of failure due to system vibrations.
Applications
Some common applications of bladder accumulators are:
• Agricultural Machinery & Equip.
• Forestry Equipment
• Oil Field & Offshore
• Machine Tools
• Mining Machinery & Equipment
• Mobile & Construction Equipment
• Off-Road Equipment
For more detailed information view the HYDAC SB Series Bladder Accumulators pages from the Womack 365 Product Catalog.
HYDAC diaphragm accumulators utilize
the compressibility of a gas (nitrogen) in storing hydraulic energy.
The gas is required because fluids are practically incompressible and
thus, can not store energy by themselves. The diaphragm is utilized to
separate the gas and the fluid sides of the accumulator.
 
The
diaphragm accumulator functions by drawing in fluid from the hydraulic
circuit when the pressure increases and thus, compresses the gas. It
returns this energy to the circuit as the pressure decreases by the
expansion of the gas.
A poppet is incorporated into the diaphragm to prevent its extrusion through the fluid port.
HYDAC manufactures two types of diaphragm accumulators:
• Welded (non-repairable)
• Threaded (repairable)
These
have been successfully applied to both industrial and mobile
applications for energy storage, maintaining pressure, leakage
compensation, and vehicle hydraulic systems (e.g. brake and suspension).
Construction
Both
types of diaphragm accumulators have the same basic construction. The
difference is in the shell. The welded version has a shell that is
electron-beam welded, and therefore cannot be repaired. The threaded
type has a shell made up of two halves (top and bottom) which are held
together by a threaded locking ring.
Diaphragm Materials
Not all fluids are compatible with every elastomer at all temperatures. Therefore, HYDAC offers the following choice of elastomers:
• NBR (Standard Nitrile)
• LT-NBR (Low Temperature Nitrile)
• ECO (Epichlorohydrin)
• IIR (Butyl)
• FPM (Fluorelastomer)
• Others (available upon request)
To determine which material is appropriate ...Always Refer To Fluid Manufacturer’s Recommendation.
Corrosion Protection
For
use with certain aggressive or corrosive fluids, or in a corrosive
environment, HYDAC offers protective coatings and corrosive resistant
materials (i.e. stainless steel) for the accumulator parts that come in
contact with the fluid, or are exposed to the hostile environment.
Mounting Position
Diaphragm
accumulators by design may be mounted in any position. In systems where
contamination is a problem, we recommend a vertical mount with fluid
port oriented downward.
System Mounting
HYDAC
diaphragm accumulators are designed to be screwed directly onto the
system. We also recommend the use of our mounting components to
minimize risk of failure due to system vibrations.
Applications
Some common applications of diaphragm accumulators are:
• Agricultural Machinery and Equipment
• Forestry Equipment
• Machine Tools
• Mining Machinery and Equipment
• Mobile and Construction Equipment
• Off-Road Equipment
For more detailed information view the HYDAC SBO Series Diaphragm Accumulators pages from the Womack 365 Product Catalog.
The new piston accumulator series: SK280 is
non repairable. The special production process of these HYDAC
accumulators saves costs. Therefore it is possible to offer better
sales prices.
• Cost-effective – because of an optimized production process
• Weight reduced series
• Reduced installation space
• Standard-gas valve with integrated M28 × 1.5 male thread (non refillable version possible)
• Quick delivery for models with standard connection
• Fully tested (function test and fatigue test)
• SAE fluid ports are available
Applications
• Mobile Hydraulic
• Industrial Hydraulic
For more detailed information view the HYDAC SK 280 Series Piston Accumulators page from the Womack 365 Product Catalog.
 FPK and FPS Series
Description
To maintain system performance HYDAC recommends that the gas precharge pressure is checked regularly. A loss in the gas precharge pressure will cause a drop in the system efficiency and could cause damage to the bladder, diaphragm, or piston accumulator.
HYDAC charging and gauging units allow hydro-pneumatic accumulators to be precharged with dry nitrogen. For these purposes, a charging and gauging unit is connected to a commercially available nitrogen bottle via a flexible charging hose.
These units also allow maintenance personnel to check the current gas precharge pressure of an accumulator. For critical systems, consider the use of a permanent gauging block which will allow constant monitoring.
All HYDAC charging and gauging units incorporate a gauge and check valve in the charging connection, and a manual bleed valve with a T-handle.
HYDAC offers two types of charging and gauging units:
- FPK - For use with gas valve version 1 (M28 × 1.5) for SBO and SK Series accumulators.
- FPS - For use with gas valve version 4 (8VI-ISO 4570) for SB, SBO and SK Series accumulators. Note: SB top repairable bladder accumulators must use FPK with FPK/SB adapter.
For more detailed information view the HYDAC Charging and Gauging Units page from the Womack 365 Product Catalog.
Rexroth hydraulic accumulators save energy and improve manufacturing
efficiency by using the accumulator as a storage device to store
hydraulic pump output flow when system demand is low and supplement
output when demand is high.
Rexroth hydraulic accumulators are used to:
- Store power for intermittent duty cycles, economizing hydraulic pump drive power
- Provide emergency or standby power
- Compensate for leakage loss
- Provide suspension in vehicles
- Dampen pulsations and shocks of a periodic nature
The majority of applications use accumulators to store energy for intermittent duty cycles or to provide a source of emergency power. In either case, the problem is determining the optimum size and pre-charge of the accumulator. Accumulator sizing is based on the gas charge. The change in gas volume and pressure determines the amount of liquid that can be added or withdrawn. However, unlike mechanical springs, compressing a gas tends to heat it, raising the pressure above what would be expected from compression alone. Expanding a gas tends to cool it, reducing the pressure below that caused by expansion alone. Either of these effects can substantially affect accumulator sizing. Expansion (or compression) of a gas resulting in a change of gas temperature produces adiabatic expansion. When an accumulator is discharged rapidly, there is not enough time for sufficient heat transfer through the accumulator walls and adiabatic expansion occurs. If the expansion (or compression) occurs slowly, there is sufficient time for heat to be added (or subtracted) by the accumulator wall to maintain a constant gas temperature and isothermal expansion occurs. The median of these two states of expansion can be partially “adiabatic”.
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