HYDAC International SBO Série Mode D'emploi page 46

5.3 Testing the pre-charge
pressure
The pre-charge pressure can be tested with or
without the FPU charging and testing unit .
On small accumulators, and wherever possible,
the pre-charge pressure should be tested
without the charging and testing unit to avoid
any nitrogen loss during the test.
NOTE
For drawings relating to the text, see fold-out
page.
The following steps relate to the use of FPU-1
(p = 350 bar). FPU-2 must be used for
0, max
higher pressures. See:
"Instruction manual Charging and testing unit
FPU"
No. 3.501.BA
Testing rechargeable diaphragm
accumulators with the charging and
testing unit FPU‑1
The following steps should be followed for
testing and charging using the FPU-1 unit.
– Diaphragm accumulators, as well as all
lines connected on the fluid-side of the
accumulator, must be released of pressure
and must remain open.
GB
– Unscrew the valve protection cap (2) from
the diaphragm accumulator.
– Slightly loosen (approx. 1/2 a turn) the int.
hex. screw (1) on the diaphragm accumulator
with an Allen key SW 6, DIN 911. To avoid
leakages on the gas side, the seal ring (3)
must be lubricated with a suitable fluid before
re-assembly.
– Screw the FPU-1 onto the gas charging
connection of the diaphragm accumulator
(M28x1.5) by hand.
– Close the release (B).
The following step is only necessary if the
accumulator must also be charged.
– Connect the nitrogen bottle (N2) with
pressure reducer (D) and adapter (G), if
required, with charging hose (F) to the
FPU-1 at the check valve (N).
Testing
– Turn the spindle (H) anti-clockwise to open
the gas valve. Once the pressure gauge (M)
indicator begins to move, turn the spindle
one more full rotation.
– Check the current pre-charge pressure on
the pressure gauge (M).
46
Charging
– The pressure setting of the pressure reducer
must not exceed the operating pressure of
the accumulator.
– Slowly open the nitrogen bottle so that the
nitrogen can flow into the accumulator.
– Interrupt the charging process from time
to time and check the pre-charge pressure
reached on the pressure gauge (M).
– Once the temperature has equalised, re-
check the pre-charge pressure and adjust
if necessary. The set values are generally
based on a charging temperature of 20 °С.
– If the pressure is too high, it can be reduced
via the pressure release (B).
– Once the required pre-charge pressure has
been reached, the int. hex. screw (1) on the
diaphragm accumulator must be closed by
turning in a clockwise direction.
– Close the shut-off valve on the nitrogen
bottle, depressurise the FPU-1 via the
release and remove the charging unit by
loosening the lock nut. Tighten (20 Nm) the
int. hex. screw (1).
– Check the sealing of the gas valve with a
suitable leak detector spray.
– Screw on the valve protection cap (2)
Testing (non) re‑chargeable diaphragm
accumulators without the FPU‑1
charging and testing unit
By setting up the accumulator as per the fold-
out page or by using the Safety and Shut-off
Block (SAF or SAB), the pre-charge pressure
can also be checked via the fluid side.
– Isolate the hydraulically-charged diaphragm
accumulator with shut-off valve  from the
system.
– Use pressure release valve  to slowly drain
the diaphragm accumulator on the fluid side.
– Watch the pressure gauge .
– The pressure will initially fall slowly. It will
drop suddenly only after the accumulator
has drained completely. This pressure is
the same as the pre-charge pressure of the
diaphragm accumulator.
– If the indicated pre-charge pressure is
different from the required pressure, the
diaphragm accumulator, if re-chargeable,
should be charged as described above.