Fresenius Medical Care 4008 E Technical Manual page 93

The temperature sensor (3) has the following functions:
– temperature compensation of the conductivity display,
– indication of the dialysate temperature.
Should the actual values (temperature or conductivity) of the dialysate exceed or fall below the
limit settings, the bypass valve (26) opens, and the dialyzer valve (24) is closed. The machine is
now in the bypass mode. The dialysate is discharged into the drain not via the dialyzer, but via the
secondary air separator (88b) and the balancing chamber (68).
If the actual conductivity and temperature values of the dialysate are within the set limits, the
dialyzer valve (24) opens. The valve (26) is closed. The dialysate flows to the dialyzer.
After the dialyzer, the dialysate which is now loaded with the substances usually eliminated with
the urine flows into the secondary air separator (88b) via a filter (73), the valve (24b) and the
blood leak detector (8). The secondary air separator (88b) comprises the pressure transducer (9)
and the level sensor (6).
With a hematocrit of 0.25, blood losses of 0.5 ml per minute are recognized in the dialysate by the
blood leak detector.
Together with the venous back pressure, the signal of the pressure transducer (9) is evaluated
and indicated on the monitor as TMP. The fluid level in the secondary air separator (88b) is
monitored by the level sensor (6). Due to the secondary air separator (88b), only airless dialysate
is always delivered into the balancing chamber (68). Any presence of air bubbles in the balancing
chamber (68) would cause balancing errors.
The dialysate is pressed into the balancing chamber (68) by the flow pump (21). As mentioned
above, the balancing chamber valves are reversed by the current rise pulses of the drive motor of
the flow pump. Using the speed of this pump, the dialysate flow can be adjusted in the dialysis
program: 300, 500, and 800 ml/min. In the cleaning programs, the flow of the dialysate is fixed.
The relief valve (78) is used to limit the pressure of the flow pump before the balancing chamber
to approx. 2 bar.
After the balancing chamber, the dialysate flows through the valve (30), the heat exchanger (77)
and the valve (87) into the drain.
The valves (86) and (87) serve to recirculate fluid during the hot rinsing and disinfection
programs.
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Fresenius Medical Care 4008 4/08.03 (TM)