Baxter Arena User manual

4. Hydraulic Theory

TABLE OF CONTENTS

4. HYDRAULIC THEORY ..................................................3

4.1 Overview............................................................ 3

4.2 Dialysate Circuit................................................ 4

4.2.1 Incoming Water Pressure Regulator ............4

4.2.2 Water On/Off Valve.....................................5

4.2.3 Heat Exchanger............................................5

4.2.4 Heater, Thermistor, Safety Thermostat........5

4.2.5 Concentrate Line Regulator(s) and
Concentrate Central Delivery Systems

(optional)...................................................6

4.2.6 Volumetric Proportioning System ...............6

4.2.7 Supply Manifold ..........................................6

4.2.8 Air Removal System ....................................9

4.2.9 "A" & "B" Rinse Fittings .............................9

4.2.10 Supply Pump Recirculation Loop..............9

4.2.11 Input Pressure Equalizer, Flow Equalizer,

and Output Pressure Equalizer................12

4.2.12 End-of-Stroke Sensors .............................12

4.2.13 Dialysate Monitoring Manifold ................14

4.2.14 Dialysate Bypass Valve and Sensor.........16

4.2.15 Rinse Block..............................................17

4.2.16 Dialysate Sample Ports .............................17

4.3 Ultrafiltration System ..................................... 17

4.4 Blood Leak Detector....................................... 18

4.5 Other Components ......................................... 18

4.5.1 Rinse Valve................................................18

4.5.2 Heat Disinfection Recirculation Valve ......19

4.5.3 Citric Acid Valve Manifold (optional) ......19

Standard Hydraulics Flow Diagram ..................... 21

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Arena Service Manual

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4. HYDRAULIC THEORY

4.1 OVERVIEW

The Arena Instrument is designed to heat incoming water to
approximately human body temperature, mix the water with
dialysate concentrate in physiologically correct proportions and
infuse the dialysate through an artificial kidney to effect
hemodialysis therapy. In doing this, it also accurately measures
the amount of fluid entering and exiting the artificial kidney and
can adjust these volumes to control the fluid removal from the
patient. Operation of the hydraulic components is controlled by
several microprocessors. Refer to Figures 4-1 and 4-2 for the
location of components in the Instrument and to the standard
hydraulics diagram (157-1278-587) at the end of this section for
thier sequence in the flow path.

4. Hydraulic Theory

Figure 4-1. Standard Hydraulics Module, Front View

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Figure 4-2. Standard Hydraulics Module, Rear View

4.2 DIALYSATE CIRCUIT

4.2.1 Incoming Water Pressure Regulator

The pressure of the incoming water is reduced and stabilized by
the adjustable water pressure regulator to the factory­recommended level (see Section 18, Calibration Procedures).

Figure 4-3. Incoming Water Pressure Regulator

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4. Hydraulic Theory

4.2.2 Water On/Off Valve

This valve is actuated through a coil using unregulated +24 VDC.
When the power is off, the valve is closed preventing water from
entering the Instrument. When power is on, the on/off valve
operation is controlled by the supply manifold level sensor signal.
During heat cleaning, the valve is closed. This valve can be
monitored using the DS1 “Flow Control” LED on the I/O
Hydraulics Power board (see Section 5, Electronic Theory).

4.2.3 Heat Exchanger

Incoming water flows through a hydraulic channel on one side of a
stainless steel plate. On the other side of the plate, the spent
dialysate flows in a countercurrent direction in an identical
hydraulic channel before draining out of the Instrument.

Heat is transferred from the spent dialysate to the incoming water
through the plate. This heat transfer preheats the incoming water,
shortening dialysate warm up time. By reducing the time the
heater is on, the heat exchanger saves energy.

The heat exchanger allows the Instrument to be used with a wider
range of incoming water temperatures since this preheating of the
incoming water reduces these variations.

Figure 4-4. Heat Exchanger

4.2.4 Heater, Thermistor, Safety Thermostat

The water is heated to the desired temperature by a heater. On the
output of the heater is a thermistor. The thermistor resistance
changes in inverse proportion to temperature changes. The
thermistor sends a signal to the UF-Proportioning Power board,
which then turns the heater on or off to maintain or increase the
temperature.

Next to the heater is a resettable thermostat, which prevents the
heater from exceeding a temperature of approximately 107°C

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4.2.5 Concentrate Line Regulator(s) and Concentrate

4.2.6 Volumetric Proportioning System

(225°F). The thermostat turns off power to the heater to prevent
damage in case of a runaway temperature circuit failure.

For testing purposes, the heater has a resistance of approximately
10-20 Ω when cold. The thermistor has a resistance of
approximately 3 KΩ at 37 to 38°C and 5 KΩ at 25°C.

Central Delivery Systems (optional)

Concentrate Line Regulators are recommended when a central
delivery system is used to feed concentrates into the Instrument.

Refer to Section 7, Dialysate Preparation, for more information.

The Instrument's volumetric proportioning system consists of fixed
volume pumps for concentrates and a fixed volume metering
device (Flow Equalizer) for dialysate. They are linked
electronically through the Ultrafiltration Controller to provide a
fixed ratio proportioning system.

Refer to Section 7, Dialysate Preparation, and Section 8,
Ultrafiltration, for more information.

4.2.7 Supply Manifold

The supply manifold controls the incoming water flow, mixes the
“A” dialysate concentrate component, removes the dissolved air
from the water, and monitors the “A” concentrate and water
conductivity. The supply manifold is composed of four
components:

• “A” Mix Chamber and Air Gap

• Air Removal Sprayer

• Air Trap and Level Sensor

• “A” Conductivity Probe/Thermistor Set

This manifold also contains the connections for the air removal
pump, and the “A” and “B” rinse fittings that connect through a
common line to the supply manifold and draw rinse water from
this source.

The “A” concentrate pump is described in Section 7, Dialysate
Preparation.

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