Pneumatic System - Breas Clearway 2 Service Manual

9 Pneumatic System

Ambient air is drawn in through filters, compressed by the blower and fed to
the patient via a proportional servo valve.
The valve spool is operated by a proportional rotary solenoid, incorporating
an angle sensor for position feedback. It has a total rotation of 110 degrees.
When it is in its fully counter-clockwise position (viewed from the spool end)
the outlet port is connected to the pressure port and the inlet to the vacuum
port, allowing full flow from inlet to outlet. This causes positive pressure at the
patient outlet.
When the valve spool is in its fully clockwise position the outlet port is
connected to the vacuum port and the exhaust to the pressure port, allowing
full flow from the outlet to exhaust. This causes negative pressure at the patient
outlet.
When the valve spool is in its central position, the spool port sits between the
pressure and vacuum ports, leaving the outlet effectively closed. This sets the
outlet pressure to zero. The pressure and vacuum ports are partially open to
exhaust and inlet allowing a flow of air through the blower to prevent
overheating.
The valve would normally work around the centre position, moving the spool
port to vary the control pressure.
Pressure measurement is made via 2 pressure transducers (for redundancy).
Output from the transducers is conditioned and used in a feedback loop for
the valve control. A fault condition will be created if a mismatch between
sensor readings or unexpected pressure at zero or a high pressure condition is
detected.
A flow transducer is fitted at the valve outlet, it is used for Cough Peak Flow
measurements, estimated volume measurements and flow control in IPPB
mode.
Pneumatic System 44
NIPPY Clearway 2 Service Manual
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2210.2657 Rev 3.0