Covidien Puritan Bennett 700 Series, Руководство по обслуживанию

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Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual 10070389 Rev. A 2-29
• The exhalation valve assembly , a pneumatically actuated valve, closes during inspiration
to prevent delivered gas from venting to the atmosphere. During exhalation, it opens
sufficiently to maintain the operator-selected PEEP. The exhalation valve is piloted by the
exhalation solenoid (in the PEEP system). The valve has an area ratio of 1.4:1. For example,
if the PEEP system provides a pilot pressure of 10 cmH
2
O, then the patient must produce a
pressure of 14 cmH
2
O to open the valve. At circuit pressures below PEEP, the valve remains
closed; at pressures higher than PEEP, the valve is opened.
• The exhalation flow sensor provides flow information on a patient’s exhaled gas. The
sensor is actually a fine mesh screen with pressure taps on both sides. The pressure taps
connect to a differential pressure transducer on the pressure solenoid PCB. Because the
flow across the screen is proportional to the pressure drop across it, the electronics can use
these pressure measurements to determine exhaled flow.
• The exhalation flow sensor pressure transducer (on the pressure solenoid PCB), a
differential type, monitors the exhaled flow. The transducer works in conjunction with
the exhalation flow sensor, described above.
Figure 2-17. Exhalation system
Exhalation system
7-00099
Exhalation
pressure
transducer
autozero
solenoid
Exhalation
valve
assembly
Exhalation
flow sensor
assembly
Exhalation
check valve
assembly
Expiratory
filter
housing
Location of exhalation system
7-00100
Exhalation
system