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Olaer Group Worldwide
Our Main Partners
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Olaer have developed solutions to master the
fluids in some twenty different business segments: aeronautical,
chemicals, defence/weapons, mining, railroad construction, Formula
1 racing, machine tools, shipbuilding, farm equipment, oil and
petrochemicals, steel mills, transportation and heavy construction,
offshore oil production and exploration. For more information,
please click on one of the following options :
.1 Reduction of installed
power
.2 Reserve power source
.3 Cushioning/springing
.4 Pulsation and pressure
shock cushioning
.5 The barrier between
media, "Transfer Barrier accumulators"
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Cost savings are the most important
arguments for installing accumulators on a system. Olaer accumulators in a hydraulic
system enable the use of smaller oil pumps and a reduction of input power. Accumulators
contribute to a lower investment cost, and on going savings in operating costs.
In systems with intermittent oil requirements or a fast cycling rate, the installation
of accumulators is often the only economic solution.
There are many different
areas of application:
Some areas of application : |
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As illustrated in the oil consumption diagram,
the three actuators have differing oil requirements. Without an accumulator one
would have to calculate the necessary pump capacity to cope with actuator III’s maximum requirement.
Using an Olaer accumulator, the pump capacity (and thereby the
installation costs) is significantly reduced. Actuator I and II’s
oil requirements are below the pump flow rate. The superfluous
volume of oil is stored in the accumulator. The flow requirement
for actuator III is greater than the pump capacity and the shortfall
is provided by the accumulator. During idle time between cycles
the accumulator is recharged.
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Die casting machines and presses often
require large instantaneous flow rates. In the same way during emergency shut
down, turbines and power plants require large uninterrupted oil supply to maintain
the hydrostatic film on the bearings. In most cases it is the same emergency shut
down system that is expected to serve as a security device, i.e. during normal
operation when the oil requirement is minimal (only leakage compensation). Without
an accumulator, a separate dedicated pump would have to be installed to circulate
this large volume of oil when the security device cuts in (perhaps once or twice
a year).
This is not an economically viable solution.
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On machine tools with several machining
heads the cutting speeds, back and forth movements, raising, cutting depth, etc.
are controlled individually.
In other words the oil flow requirement may widely fluctuate.
When an accumulator is installed on each machining head, the fluctuations
in oil demand are met and higher start up speeds can be allowed
as the inertia associated with accelerating the oil is overcome
faster than from a pump located at a distance.
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Efficient production using presses and stamps is dependent on
high supply speeds whilst the actual work process takes place
at low speed and high pressure. See diagram.
During supply, pump I (the low
pressure pump), pump II (the high pressure pump) and the accumulator
work in tandem so that the required high speed is reached. With
the increase of pressure towards the end of the stroke, valve
A shuts and only pump II continues to yield a small flow of oil
at high pressure, while pump I recharges the accumulator. |
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When a specific pressure in an hydraulic
system has to be maintained over a longer period of time (e.g. in order to keep
a throttle valve open, in for example clamping devices or pressure test devices)
compensation must continually be made for losses due to leakage. For this purpose
a small pump unit with an accumulator is used. As soon as the accumulator has
been emptied to the minimum required pressure, the pump cuts in via a pressure
transmitter and the accumulator is refilled. When the maximum pressure is reached
the pump cuts out automatically.
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Accumulators maintain the pressure between
two cylinders over a longer period of time. Once the correct compression
pressure has been reached the pump can immediately be redirected
to other actuators. The accumulator maintains the necessary pressure
throughout the whole process.
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Rather than the kinetic energy being transformed into heat, it
is stored in an accumulator which then releases the energy as
required. This application can also be found in presses where
oil during the piston’s downward stroke is stored under
pressure in the accumulator and then used later in the piston’s
upward stroke.
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Accumulators are often installed
as safety devices. Without an accumulator, a power failure results
in machinery stoppage. Accumulators can deliver some oil flow
for a specific period of time thus protecting valuable machinery,
plant and not least human life.
Some areas of application: |
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| .2.1
Hydrostatic bearing
During machine operation, the hydrostatic
bearings must remain under pressure. In the case of power failure
the oil pressure pump stops and the necessary pressure to the
bearing can no longer be maintained. Accumulators insure the necessary
minimum pressure as the machine slows to a halt and in this way
prevents expensive damage being caused to the bearings.
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Supply of lubricating oil
Bearings on larger machines such as turbines, compressors,
water pumps etc., require continuous circulation of oil. In the event of a power
failure, a back-up pump cuts in, driven by another power source (e.g. a diesel
motor). Nonetheless, a few seconds pass before the back-up pump cuts in and the
flow of lubricating oil will cease for that period. Accumulators guarantee that
the work already in process continues, valuable machinery is protected from damage
and downtime is reduced to a minimum.
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Safety devices are installed in order to carry out a specific
task in case of a power interruption. For example, on servo valve
actuators in offshore processing plants and control systems, on
blockout preventer, or the opening and closing of high voltage
circuit breakers. In all these cases the accumulator does not
operate whilst the plant is in operation. It remains full at all
times and the stored energy is always available.
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Accumulators are used for the emergency
use of brakes on winches, mountain railways, etc. The accumulator is during operation
or shut down. It is therefore always charged ready to perform an emergency braking.
Very often the operation takes place in reverse, i.e. braking occurs whilst the
spring power and brake cylinders are held open against a spring power with the
aid of the accumulator.
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Because of the way it is built,
each accumulator is a spring. The stiffness (the pre-charged pressure)
can therefore always be simply adjusted. This allows the following:
Some areas of application |
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The tool head’s weight on machine
tools can be adjusted by an accumulator without sluggishness in
a small space. Compared to weight adjustment using chain and dead
weights, a hydraulic weight adjustment using accumulator and cylinder
has the following advantages:
economy of weight, reduced load
on the base, smaller use of space, easier transport and adjustment possibilities
through the altering of the precharge pressure.
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| .3.2
Chain, belt or cable tightening
Drive chains etc., on machines can be tightened “softly”
with the help of an accumulator. Impact from the drive chain is
not transferred to the machine, but cushioned by the accumulator.
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Railroad cables and cables pulling ski
lifts etc., must be precisely tightened. The cables’ length
varies, however, with the speed of the car and thermal expansion.
Accumulators adjust the length and keep the tension within tolerances.
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Mechanical stress due to driving over bumps
or into barriers (e.g., forklift truck, snow plough) is absorbed
by the accumulator. This enables a safe and gentle transportation
of the load, higher driving speeds, reduced risk of accidents
and a longer life span for the vehicle.
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A hydro-pneumatic cushion increases the
vehicle’s security, softens jolts, reduces strain on materials
and thereby reduces operation costs.
Some areas of application : |
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Greater and greater demands are
being placed on today’s machines to increase their performance
output levels. This leads to problems of shocks, pulsations and
vibration, factors that increase the noise level and reduce equipment
life. Pulsation dampers accumulators are therefore installed in
high frequency systems.
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Pulsation from piston pumps produce noise and vibrations and can
disturb the controllers. In the same way servo valves can also
start to hunt at an undesirable level.
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It is not always possible to operate valves softly in machines
with a high cycling rate. Accumulators used as “Pulsation
damper” type, absorb the shocks that take place during spool
transitions.
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When large quantities of oil are sporadically discharged in the
return line this causes fatigue damage to the oil coolers and
filters. Pressure surges also take place when sudden flow is delivered
at high speed into a system, or when the oil flow is instantly
stopped by a valve. Accumulators absorb such shocks, cushion them
and stabilise the whole system pressure.
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Pressure surges cannot always be cushioned where they occur. It
is also often difficult to find out their cause. Pressure waves
spread throughout the entire hydraulic system. By installing an
accumulator the pump and control valves are protected against
these shock waves.
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On large water and process systems, tremendeous surges
often occur during pump startup or shut down as well as when emergency
valves are actuated. The use of large alleviators located next
to the pump or the valve reduce the intensity of the shock while
avoiding effects of column separation.
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In the same way as the piston
accumulator, the “Transfer Barrier” accumulator enables
the transfer of pressure from one medium to another without mixing the different
media together. These types of accumulators are also used when large amounts of
gas are needed for the accumulator to be able to provide a specific volume of
oil when pressure differential is low.
Some areas of application : |
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Gas cylinders are supplied with the maximum pressure of 250
bar. This is often insufficient (e.g. for high pre-charge pressure in accumulator).
With the help of a hydraulic unit and a “Transfer
Barrier" accumulator or a piston accumulator you get a simple
booster. The gas is filled from the cylinder into the accumulator and is compressed
from the other side using an oil pump into the pressure receiver. Using a set
of check valves on the gas side and a valve operated by a limit switch on the
oil side, this cycle is repeated as often as required in order for the necessary
gas pressure to be built up.
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Compressors are often used with mechanical seals. The pressure
in this seal fluid must lie at 0,5 - 1 bar above the gas pressure
in the compressor. In petrochemical plant the gas in the compressor
is not mixed with the seal fluid. A tank which lies 5-lO in above
the seal is filled with a neutral fluid and pressurised by the
gas in the compressor. Furthermore a “Transfer Barrier”
accumulator is connected between these and separates the two fluids
completely.
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With machines which operate pneumatically it is often advantageous
for some of the operations to be carried out hydraulically. “Transfer
Barrier” accumulators separate the air from the oil and
make an extra hydraulic power pack redundant.
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Pressure testing (e.g. pressure pipes) is most often carried
out with water, in order that the entire equipment doesn’t
get polluted with oil in case of leaks or rupture. To ensure that
stainless steel power unit is not necessary, a common hydraulic
unit can be used combined with a “Transfer Barrier”
accumulator.
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Often in a number of hydraulic power units only small pressure
differentials are allowed. When large instantaneous flow rates
are required (i.e. rolling mills), the gas volume required becomes
extremely large. Plant costs can be reduced if “Transfer
Barrier” accumulators or piston accumulators connected to
gas bottles are installed.
In underwater systems the operating unit can be subjected to high
pressure differential. Installation of an accumulator in “Transfer
Barrier” form, guarantees pressure equalisation at all depths
of water.
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