Theory of operation
2-74
10070389 Rev. A
Puritan Bennett™ 700 Series Ventilator System Service Manual
Figure 2-60. Exhalation and piston retraction parameters
PEEP + 10 cmH
2
O
P
cyl
P
e
30 psi
29 ps
i
Air
Oxygen
When the exhalation valve opens,
P
e
falls, then is maintained at
PEEP.
When the exhalation valve is
opened, exhaled flow is recorded.
Piston retraction begins once
exhalation is declared. In this case
the high-flow oxygen solenoid is
energized, causing a slight dip in
oxygen source pressure. During the
first part of the retraction period,
oxygen, flowing at 150 L/min, enters
the cylinder, which is also retracting
at -150 L/min. During the second part
of the retraction period, room air is
drawn in at 150 L/min, creating an
air/oxygen mixture of 61%.
0 L/min
When the inspiratory time has
passed, exhalation is triggered. The
exhalation solenoid is de-energized,
opening the exhalation valve.
0 L/min
7-00168
High-flow solenoid flow
+ piston retraction
= 150 L/min + (-150 L/min)
= 0
Retraction speed
≈ -150 L/min
High-flow oxygen
solenoid flow 150 L/min
High-flow
oxygen
solenoid
Oxygen
source
solenoid
Exhalation
flow
Exhalation
solenoid
Piston
velocity
Exhalation
trigger
Summary of Contents for Puritan Bennett 700 Series
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