Arena Service Manual
pressure pump recirculation loop at a rate higher than the rate of
flow through the Instrument.
The pressure and flow generated by this pump are to fill and
equalize the pressures in the flow equalizer. The DP pump
supplies the spent side of the flow equalizer with a mixture of
spent dialysate and ultrafiltrate.
8.3.10.2 UF Removal Regulator
The DP pump flow is constrained by the Input Pressure Equalizer,
creating a positive pressure that is regulated by the UF removal
regulator, which is used to control the filling of the UF flow meter.
This regulator controls the pressure from the DP pump
Recirculation loop between 200 and 300 mmHg at the input to the
UF flow meter.
8.3.10.3 UF Flow Meter
The UF flow meter is a measuring device composed of a precisely
measured chamber with a small diaphragm separating it into two
compartments. Each compartment has 2 two-way valves
connecting it to either the flow path or the drain. The UF flow
meter is connected into the flow path in the dialysate pressure
pump recirculation loop, right after the UF removal regulator.
A compartment fills when the UF-Proportioning Power board
opens its valve to this positive pressure environment. When one
compartment is filling, the second compartment is emptying to the
drain. Based on the calibrated volume of the UF flow meter, the
UF-Proportioning Controller board can control precise amounts of
fluid by sending a calculated number of open/close signals per
minute to the valves. The rate of fluid removal is determined by
the ultrafiltration information entered into the Instrument by the
operator. The Instrument calculates the number of times per
minute each valve must cycle to equal this UF volume.
For example:
At an UF rate of 600 mL/hr, 10 mL/min must be removed.
Therefore the 1.5 mL UF flow meter compartment is filled
(cycled) every 9 seconds.
To summarize, the flow path from the fresh dialysate
compartments of the flow equalizer to the dialyzer and back to the
spent dialysate compartments of the flow equalizer is a closed
system except for two openings. One opening is the dialyzer; the
other is the UF flow meter. When the volume in the dialysate
pressure recirculation loop is reduced by solution being removed
through the UF flow meter, a pressure drop is exerted on the
dialyzer.
8-16 157-1278-915 Rev A
January 2004
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