Covidien Puritan Bennett 700 Series, Service Manual

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Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual 10070389 Rev. A 2-81
2.8.3 Safety valve open (SVO)
The ventilator’s safety valve provides a way for the patient to breathe unassisted in cases
where a hardware or software failure might compromise safe ventilation. In most such cases
(except where the UI and BD microprocessors are unable to control the safety valve due to a
malfunction), the UI or BD microprocessor places the ventilator into the safety valve open
(SVO) state. Figure 2-64 is a pneumatic diagram showing the ventilator in the SVO state.
The SVO state involves these actions:
• The safety valve solenoid is de-energized under control of the UI or BD microprocessor,
causing the safety valve to open, so the patient can breathe room air.
• The SAFETY VALVE OPEN indicator is lit and the alarm is sounded.
• The PEEP pump drive is disabled, causing the exhalation solenoid to be de-energized. This
results in the exhalation valve being opened.
• The drive to the motor/encoder is disabled, reducing the circuit pressure to zero.
The SVO state can also be triggered by a backup hardware circuit on the pressure solenoid
PCB. If neither microprocessor is able to control the safety valve, the backup circuit opens the
safety valve when pressure exceeds 115 cmH
2
O. Table 2-4 summarizes the events that cause
the safety valve to open.
Table 2-4: Safety valve open causes and indications
Trigger Audio alarm Status indicators Notes
Ventilator
inoperative
condition
(including
patient system
pressure
exceeded
92 cmH
2
O)
Backup alarm
(possibly main
alarm) SAFETY VALVE
OPEN
VENT INOP
ALARM (solid or
flashing) Hardware failure (pressure sensor or
pressure sensing circuit, motor,
memory, microprocessor, or DC power
failure; inspiration manifold
temperature < 5 °C; or three software
resets in 24 operational hours)
resulted in software declaring a VENT
INOP condition.
Patient system
pressure
exceeded
115 cmH
2
O
Indeterminate SAFETY VALVE
OPEN Safety valve was opened by backup
circuit on pressure solenoid PCB. Valve
should have been opened by primary,
microprocessor-controlled circuit at
92 cmH
2
O.
Occlusion Main alarm SAFETY VALVE
OPEN
ALARM
(flashing) Safety valve opens and closes to
relieve pressure.
POST execution Both main and
backup alarms
for a time SAFETY VALVE
OPEN Because the ventilator’s functionality
is unknown until POST is completed,
the safety valve remains open (de-
energized) during POST.