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1. Accumulators
Short term Storage:
When stored in a stable, non-severe environment,
accumulators can be left in their original packing for a number
of weeks without fear of deterioration.
Long Term Storage:
If the units are to be stored for longer periods
of time, it is important that the bladder is maintained in its
natural, unstressed shape within the body and that any deterioration
of components through corrosion is prevented.
We advise that accumulators be filled with
system (or preservation) fluid to exclude air from the shell
cavity and prevent condensation. This is especially
important where the system fluid is of low viscosity e.g. water
based. (see COMMISSIONING).
Procedure:
Exhaust any existing pre charge pressure from
the bladder and remove the valve core. Then replace the valve
core and cap to maintain atmospheric pressure within the bladder.
Invert the accumulator, fluid port upwards,
and fill with system fluid until the residual space between
bladder and shell is filled. In certain circumstances it may
not be desirable (or safe) to use the system fluid. In this
case a compatible fluid should be used for preservation.
Seal off the fluid port opening with a pressure-tight
plug.
This procedure is a general recommendation
only. Where severe conditions are prevalent special precautions might be need
to be considered.
2. Spare bladders
All rubber compounds specified by Olaer Fawcett
Christie fall into the category of low susceptibility or high
resistance to deterioration by ageing.
Details of material classification and shelf
life expectancy can be found in BS3574: 1989 and our Technical
Specifications, TechSpec 105.
Ideal storage conditions:
Stored under ideal conditions bladders have
an expected shelf life of 5 years.
- Stored in a stress-free condition either
due to natural shape or by partially inflating to natural size
using nitrogen gas.
- At temperature between -5ºC and +5ºC.
- In a "Valeron" packaging away
from heat or rotational electrical equipment. This special packaging
is designed by OLAER, and available on request.
Storage conditions less than
ideal:
Where ideal storage conditions cannot be met,
bladders have an expected shelf life of 1-3 years if they are
stored as follows:
- Stored in a stress-free condition due to
natural shape or by partially inflating with compressed air
or nitrogen gas, so that they stand lay flat without bending
or folding. Bladders should not be stacked.
- At temperature up to 25ºC.
- Stored in darkness either in a dark room
or covered with clean, opaque polythene and away from direct
sunlight, heat or rotational electrical equipment.
Inspection before use:
- Inflate to not more than 1½ times
natural diameter.
- Visually examine seams for defects and surface for crazing.
- Immerse in water to inspect for leakage or perforations.
NOTE: Bladders not stored properly
will be subject to attack from ozone, heat or UV light. Cracking
will develop within one year.
For full details of storage recommendations
for bladders refer to our technical Specification, TechSpec
105.
1. Inspection of accumulator
All OLAER Fawcett Christie accumulators are thoroughly inspected
prior to despatch from our factory and are ready for installation
following pre charging.
After unpacking the accumulators, inspection
of the accumulators is recommended for possible damage during
transit. The following items should be checked:-
a) check the following items for tightness
: all nuts, screws, locking rings, bleed screws, adaptors and
fittings, as applicable.
b) check that the maximum pressure of the
accumulator is equal to or greater than the maximum pressure
of the system.(see interpretation of markings).
2. Installation
recommendations
a) All accumulators are supplied un-pre
charged from the factory unless requested. Prior to applying
hydraulic pressure to the system all accumulators must be pre charged with nitrogen
(for pre charging see commissioning).
b) It will be necessary to check the gas pre
charge pressure at regular intervals (see routine maintenance).
Consideration should therefore be given to the following:
- the provision of a safety block fitted between
the accumulator and fluid pressure line to enable isolation
of hydraulic system pressure.
- the location of the gas charging valve with
regard to the potential for accidental damage and safe discharge
of high-pressure gas.
- the provision of a warning label (in addition
to that provided on the accumulator nameplate) stating "PRECHARGED
WITH N2 GAS AT ....BAR".
It is necessary to ensure that the accumulator
is protected from overpressurisation. General protection is
usually provided by the hydraulic system relief valve, which should be set at
no higher than 10% above the maximum working pressure (MWP) of the accumulator.
Specific protection for the accumulator can be provided in the following ways:
- a hydraulic relief valve located in a safety
block will prevent both liquid and gas side overpressurisation.
- a fusible plug will relive gas side pressure
in the event of a fire.
- a burst disc will relieve gas side overpressuriation.
On storage applications a check valve fitted
between pump and accumulator will ensure non-reversal of the
pump.
For maximum efficiency and service life, accumulators
should be mounted vertically where possible, fluid port facing
down.
For fluid port and gas connection threads
see our catalogue. If it is necessary to adapt to another size,
special adaptors are available.
A range of clamps, support brackets and other
accessories are available to assist in installation. Their use
is strongly recommended.
Please contact
our technical department for advice.
Important notes
1. Use only oxygen-free, dry nitrogen gas.
2. All accumulators are supplied un-pre charged unless a pre charge pressure is
specified when ordering. Prior to applying hydraulic pressure to the system all
accumulators must be pre charged with nitrogen.
3. Check details of accumulator
on label and shell for maximum working pressure. The maximum hydraulic pressure
must not exceed the MPW of the accumulator.
4. Always use the nitrogen pressure
regulator valve when accumulators shell pressure rating is lower than gas pressure
in nitrogen cylinder.
5. Pre charges vary with operating conditions. check
with our technical department if no pre charge has been previously recommended.
For a guide the following values can be used :
- storage application : 90%
of minimum allowable system pressure
- shock application : 60% of flow pressure
at accumulator position
- pulsation damper : 70% of mean pumping pressure
NB : Allowing pre charge to fall below 20% of maximum system pressure may cause
premature failure of the bladder.
- Ensure that the bladder and shell inner
are adequately lubricated with system fluid before commencing pre charging. This
is especially important where the system fluid is of low viscosity eg water based.
Pre charging procedure
The following procedure should be adopted
for safe pre charging of accumulators. All pre charging equipment
specified is detailed in our catalogue.
For accumulators having a shell working pressure
less than the nitrogen source, refer to fig 2.
For accumulators having a shell working pressure equal to or
greater than the nitrogen source refer to fig.3.
For accumulators fitted with a back-up-bottle
or remote charging point, refer to fig.5.
For high-pressure accumulators the gas valve
is fitted with a replaceable 'Schraeder-type' core. Ensure that
this is correctly tightened before attempting to pre charge.
Procedure 1.- Using a nitrogen pressure
regulator
1. Remove protective cap(1) if fitted
and sealing cap (2).
2. Attach regulator(3) to nitrogen cylinde(4).
3. Attach charging set (5) to accumulator gas valve assembly(6)
and connect charging hose (7) between regulator (3)and charging
set connection.
4. Back off regulator handle (8)anti-clockwise until loose,
check gas bleed valve (9) on charging set is closed and screw
hand wheel (10) clockwise to open gas valve. Do not screw knob
down tight.
5. Open nitrogen cylinder valve by turning key (11), cylinder
pressure will register on right-hand gauge (12) . this pressure
should be checked against the required pre charge pressure.
6. Turn handle (8) clockwise until outlet pressure on left-hand
gauge (13) registers 10% higher than required pre charge pressure.
When pressure ont he charging set and outlet gauges are equal,
close nitrogen cylinder cap.
7. Turn hand wheel (10) anti-clockwise to seal gas valve.
8. Crack bleed valve (9) to exhaust gas from charging hose and
remove hose from charging set and replace hose connection sealing
cap.
9. Close bleed valve, turn hand wheel (10) clockwise to open
gas valve. Do not screw knob down tight. Crack bleed valve (9)
to vent down to required pre charge pressure. Close bleed valve.
10.Turn hand wheel (10) anti-clockwise to reseal gas valve,
crack bleed valve and remove charging set from accumulator.
11. Test gas valve for leaks using a leak detection spray or
a soapy water solution.
12. Replace sealing cap (2), tighten with pliers, and protective
cap if fitted.
Procedure
2.- Nitrogen pressure regulator not required fig 2,3,4.
1. Remove protective cap (1) if fitted and
sealing cap (2).
2. Attach charging set to accumulator gas valve assembly(6).
3. Connect charging hose (7) to nitrogen cylinder (4) using
the appropriate adaptor, and attach the free end to the charging
set.
4. Turn hand wheel (10) clockwise to open gas valve> Do not
screw knob down tight. Slowly open nitrogen cylinder by turning
key(11).
5. Allow pressure on the gauge (14) to read slightly in excess
of required pre charge and then close nitrogen cylinder valve.
6. Turn hand wheel (10) anti-clockwise to seal gas valve.
7. Crack bleed valve (9) to exhaust gas from charging hose and
remove hose from charging set and replace hose connection sealing
cap.
Procedure 3.- Permanent charging set
fitted fig.4
Follow step of procedures 1 or 2 as appropriate
but connect to the permanent charging set as shown in fig4.
When a new accumulator has been in service
for a short period, the pre charge should be checked to ensure
there is no leakage. Subsequent checks should need only be at
6 monthly intervals.
When checking the pre charge of an accumulator
installed in a system, the accumulator must be isolated from
the system pressure and the fluid removed by carefully opening
the bleed valve and collecting the fluid in a suitable receptacle.
Alternatively, shut the system down and release the fluid pressure
back to tank.
Fit a charging set (without charging hose)
ensuring the bleed valve is closed and cap is fitted to the
charging connector.
Turn hand wheel clockwise and check pre charge
NB : Do not screw knob down tight.
Replenish if required, following steps of
procedures 1 or 2 appropriately.(see commissioning)
1. Re-certification for continued safe use
In Australia most gas-loaded accumulators fall within the requirements
of the AS3788 pressure equipment in service inspection.
Key points of this standard include :
- requirements to determine the safe operating
limits of the accumulator and record the fact that these are
not exceeded by the system pressure.
- preparation of a written scheme of examination for accumulators
used to store energy above certain limits.
establishing a maintenance procedure and carrying out regular
safety checks and examinations.
Full details can be found under re
certification
Please refer to bottom
/ top repairable assembly
unit.
Cleaning and inspection
1. Clean all metallic components with an organic
solvent.
2. Inspect the condition of all components within the fluid
port.
3. Check the fluid port poppet valve to ensure free movement.
4. Inspect the bladder for any visible signs of damage. (cracking
or surface abrasion)
5. Inspect the shell, both inside and outside for signs of corrosion.
6. Replace any parts found or considered to be defective.
7. Replace the following parts irrespective of condition : anti
extrusion ring, 'O' ring, back-up ring,'O' ring.
NB : the 'heart' of a bladder accumulator
is the bladder itself. OLAER Fawcett Christie strongly recommend
that all elastomeric components are replaced during servicing/re-certification.
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