Arena Service Manual
Instead of the bucket, the water volume is measured by the
volumetric flow equalizer. This volumetric flow equalizer fills
with a very precise volume of fluid and the Instrument knows this
volume. Based on the flow rate and the concentrate type, the
Instrument calculates the amount of the acetate or acid and
bicarbonate required per stroke of the flow equalizer. The rest of
the flow equalizer volume is filled with water resulting in a
properly proportioned dialysate.
7.3.2 “A” and “B” Concentrate Reciprocating Rotating
Piston Pumps
The acid (or acetate for acetate dialysis) concentrate is pumped
from its container into the air gap chamber through a fixed volume
reciprocating rotating piston pump called the “A” concentrate
pump and the pink concentrate line.
The bicarbonate (or a mixture of acetate and water recirculated in
acetate dialysis) concentrate is pumped from its container through
another fixed volume reciprocating rotating piston pump called the
“B” concentrate pump, and the blue concentrate line.
These pumps are controlled by a stepper motor that is
automatically adjusted to turn a precise number of rotations per
minute. The pump delivers a fixed volume of concentrate each
revolution. The motor is coupled to the piston of a precision
ceramic pump. As the piston rotates it moves in and out of the
cylinder, alternately drawing in fluid through one port and
discharging it through another port.
Figure 7-5. Reciprocating Rotating Piston Pump
7-8 157-1278-914 Rev A
January 2004
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