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Diaphragm Accumulators
Fluids are practically incompressible and
cannot therefore store pressure energy.
The compressibility of a gas is utilised in
hydraulic accumulators for storing fluids.
HYDAC diaphragm accumulators are
based on this principle, using nitrogen as
the compressible medium.
A diaphragm accumulator consists of a
fluid section and a gas section with the
diaphragm acting as the gas-proof screen.
The fluid section is connected to the
hydraulic circuit so that the diaphragm
accumulator draws in fluid when the
pressure increases and the gas is
compressed. When the pressure drops,
the compressed gas expands and forces
the stored fluid into the circuit.
At the base of the diaphragm is a valve
poppet. This shuts off the hydraulic outlet
when the accumulator is completely
empty and thus prevents damage to the
diaphragm.
NOTE:
HYDAC diaphragm accumulators when
fitted with a HYDAC Safety and Shut-off
Block comply with the regulations of the
Pressure Equipment Directive
PED 97/23/EC and the German
regulations on health & safety at work
(Betr.Sich.V.).
See catalogue section:
zzSafety and shut-off block SAF/DSV
No. 3.551
1.2.t Design
HYDAC diaphragm accumulators are
available in two versions.
1.2.1t Weld type
int. hex. locking screw
pressure vessel
diaphragm
valve poppet
valve body
This consists of:
zzWelded pressure vessel, rechargeable
on the gas side or, alternatively,
completely sealed. Fluid connection
available in various types.
zzFlexible diaphragm to separate the fluid
and gas sections.
zzValve poppet set into the base of the
diaphragm.
1.2.2t Screw type
int. hex. locking screw
pressure vessel
1.2.3t Diaphragm materials
The diaphragms are available in the
following elastomers:
zzNBR (acrylonitrile butadiene rubber,
perbunan),
zzIIR (butyl rubber),
zzFKM (fluoro rubber, Viton®),
zzECO (ethylene oxide epichlorohydrin
rubber).
The material must be selected according
to the particular operating fluid and
temperature.
When choosing the elastomer, allowances
must be made for the fact that the gas
can cool down to below the permitted
elastomer temperature if there are adverse
discharge conditions (high pressure ratio
p2/p0, high discharging velocity). This can
cause cold cracking in the elastomer.
The gas temperature can be calculated
using the HYDAC Accumulator Simulation
Program ASP.
1.2.4t Corrosion protection
For use with chemically aggressive fluids
the accumulator can be supplied with
corrosion protection, such as plastic
coating or a galvanic or chemical surface
protection. If this is insufficient, then almost
all types can be supplied in stainless steel.
1.3.t Mounting position
Optional. However, if there is a risk of
contamination collecting, a vertical position
is preferable (fluid connection at the
bottom).
diaphragm
valve poppet
valve body
This consists of:
zzForged upper section with gas charging
connection.
zzForged lower section with fluid
connection.
zzExchangeable flexible diaphragm to
separate the gas and fluid.
zzVulcanized valve poppet set into the
base of the diaphragm.
zzLock nut to hold the upper and lower
sections of the accumulator together.
E 3.100.24/03.12
1.tDESCRIPTION
1.1.tFunction
55
"
