Covidien Puritan Bennett 700 Series, Service Manual

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Theory of operation
2-22 10070389 Rev. A Puritan Bennett™ 700 Series Ventilator System Service Manual
• The exhalation Positive End Expiratory Pressure/Continuous Positive Airway Pressure
(PEEP/CPAP) solenoid is a three-way valve that selects the pneumatic source for piloting
the exhalation valve. The solenoid is energized during all inspirations to provide
exhalation valve pilot pressure via the inspiration manifold. When de-energized (during
exhalation), the valve uses the pressure from the PEEP pump as its pilot source.
• The safety valve functions primarily to relieve overpressure in case of ventilator failure or
an occlusion, and to allow patient breathing in case of total ventilator failure, such as
complete loss of power. It has other functions; these are detailed in Section 2.8.3. The
normally open valve is opened either under software control or via a dedicated circuit, as
a backup.
The safety valve includes a solenoid actuator that is normally energized (closed) while the
ventilator operates. The closed valve prevents gas from escaping to the room and thus
allows the ventilator to deliver gas through the inspiration manifold to the patient. When
the solenoid is de-energized, and the safety valve poppet lifts open via the return spring,
opening the ventilator breathing circuit to atmosphere.
2.2.3.2 Operational description
During the breath delivery phase, mixed gas from the cylinder flows through the inspiration
manifold toward the patient. This inspiration gas also flows through the exhalation solenoid;
this gas pressure pilots the exhalation valve closed during inspiration.
During exhalation, the exhalation solenoid routes PEEP pilot pressure to pilot the exhalation
valve open as necessary to maintain PEEP.
If the software places the ventilator into the safety valve open (SVO) state (for example, if
system pressure exceeds 92 cmH
2
O) or if either the cylinder or patient pressure exceeds
115 cmH
2
O, the safety valve solenoid is de-energized. The patient can then breathe room air.
See Section 2.8 for a description of the SVO state.