Gambro AK 95, Service Manual

Page: 32 / 247

AK 95 / AK 95 S Service Manual
HCEN 9134 Rev. 10.2005
Technical Description
2:11
The treatment is carried out under controlled
ultrafiltration, UF. The
UF- volume is a meas-
ure of the ultrafiltrate. The differential flow is
measured in the
UF measuring cell . The
required UF-rate is selected by setting the
treatment time and the UF-volume. The actual
UF-rate is compared with the required UF-rate
and the
suction pump is regulated so that the
desired UF-rate is obtained. If the actual value
is lower than the required value, the suction
pump will run faster. When the operator adjusts
the UF- volume or treatment time, the system
automatically calculates the UF-rate.
Every 30 minutes during treatment, the UF-cell
is automatically self-calibrated. This is called a
taration . This has to be done because waste
products in the fluid returned from the dialyzer
will be deposited in layers on the inside of the
measuring channel 2. The taration can be
divided into two phases:
Phase 1: Offset (Zerosetting) phase. The UF
measuring cell and the dialyzer are “discon-
nected”, i.e. there is no fluid passing through
neither of the two channels in the UF cell. The
offset of the two measurement channels can now
be measured.
During this phase the DIVA, BYVA and TAVA
valves are closed and the ZEVA valve is open.
The pressure in the flow path is controlled by
the suctionpump. The HPG-pressure is used and
the set value is the pressure measured just
before start of the self-calibration.
Phase 2: Coefficient (flow deviation) phase. The
dialysis fluid is led past the dialyzer but through
the UF unit, i.e. the same amount of fluid is
passing through both channels of the UF cell.
The DIVA, TAVA and ZEVA valves are closed
and the BYVA valve is open. The calibration
coefficient of channel 2 can now be calculated,
channel 1 is reference.
The taration takes totally about 60 seconds.
When the taration is completed, the treatment is
resumed.
Before the UF measuring cell there is a pres-
sure transducer, HPG (high pressure guard).
INVA is closed if the pressure measured by the
HPG transducer is above or equal to +550 mmHg
(presetable).
Fluid part, continued:
The degassing chamber is used to separate air
from the dialysis fluid. A negative pressure is
created by means of the
flow restrictor to-
gether with the flow pump. This degassing
pressure is presettable between -400 mmHg and
-700 mmHg, to adjust the degassing on high
altitudes.
The air expands in the expansion chamber . A
draining restrictor is integrated in the botton
of the expansion chamber.
The degassing pressure transducer , which
measures the negative pressure, is used to
control the flow pump in order to ensure the
correct degassing pressure. The air bubbles are
separated in the
degassing chamber . When the
fluid level in the degassing chamber reaches the
minimum level depending on increased air
pressure, the float valve in the degassing cham-
ber is opened and the air is led from the
degassing chamber to the drain via the suction
pump. When the fluid level in the degassing
chamber reaches the maximum level, the float
valve is closed. The dialysis fluid is taken out in
the bottom of the degassing chamber. The
rinsing valve,
RIVA , is closed during treatment.
During disinfection the rinsing valve is open, in
order to fill the degassing chamber completely.
The flow restrictor is also used to control the
main flow in the system. The main flow is vari-
able between 300-700 ml/min in steps of 20 ml/
min. The degassing restrictor valve,
DRVA , is
regulated to achieve correct flow. During disin-
fection and rinse this valve is completely open.
The third conductivity cell, Cond.Cell P , is only
used for the protective system.
There is a temperature transducer in the con-
ductivity cell to compensate the conductivity
calculation since it varies with temperature,
approxi1,8 % per °C.
Figure 6. Flow pump and degassing chamber