2 Theory of Operation
1006-0453-000 05/04
2-25
Figure 2-16 • Exhalation manifold
2.5.4 Drive Gas Check
Valve (DGCV)
The Drive Gas Check Valve (DGCV) is used downstream of the flow control
valve to create the pilot pressure for closing the exhalation valve during
inspiratory phases, The DGCV valve is biased shut by an integral weight that
supplies approximately 3.5 cm H
2
O of bias pressure before permitting flow
downstream to the breathing circuit. When the ventilator is exhausting flow
from the breathing circuit, the DGCV permits the exhalation valve pilot
pressure to be de-coupled from the circuit pressure. This permits the
exhalation valve to open and lets gas flow to the exhaust and the gas
scavenging system.
2.5.5 Bellows Pressure
Relief Valve
The Bellows assembly is the interface between drive gas and patient gas in the
breathing system. The exhalation valve and pressure relief valve (or pop-off
valve) in the bellows assembly control the pressure in the two gas circuits and
exhaust drive gas and excess fresh gas.
The Bellows Pressure Relief Valve (PRV) is normally closed, maintaining
approximately 1.5 cm H
2
O in the breathing circuit in a no flow condition,
enough to keep the bellows inflated. It is piloted closed during inspiration and
remains closed until the bellows is refilled during exhalation. It will exhaust
≤ 4 L/min excess fresh gas flow at ≤ 4 cm H
2
O.
BLEED RESIST0R
EXHALATION
VALVE
BREATHING CIRCUIT
BELLOWS
EXHAUST TO
SCAVENGING
SYSTEM
DRIVE GAS
CHECK VALVE
REGULATOR
25 psi
CONTROL
FLOW
VALVE
VENT TO
ROOM AMBIENT
ATMOSPHERE
GAS INLET
VALVE
5 MICRON
INLINE INLET
FILTER
SUPPLY GAS
35-100 psi
PRESSURE
RELIEF
FLOW
TEST
POINT
MECHANICAL
OVERPRESSURE
RELIEF
110 cm H2O
DIFFERENTIAL
PRESSURE
RELIEF
30 cm H2O
TO DRIVE PRESSURE
LIMIT SWITCH
100 cm H2O
TO MANIFOLD
PRESSURE
TRANSDUCER
ATMOSPHERE
FREE BREATHING
CHECK VALVE
AB.29.088
Summary of Contents for Aestiva 7900 SmartVent
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