Ventilator Pneumatic - O
2
Drive Gas Theory of Operation
1 - 36 0070-10-0683 AS3000™ Service Manual
1.8 Ventilator Pneumatic - O
2
Drive Gas
1.8.1 Ventilator pneumatic drive
Oxygen is the driving gas for the ventilator. In addition to the flowmeter block, a high
pressure regulator reduces the supply pressure to 25.4 psi (175 kPa). This pressure
represents the drive gas for the ventilator.
The drive pressure regulator is placed ahead of the proportional valve that generates the
driving gas flow during the inspiratory phase. This flow fills the bellows dome that surrounds
the bellows.
1.8.2 Drive Pressure-High pressure regulator
The drive pressure regulator stabilizes the supply pressure provided to the proportional valve.
The flow generated by the proportional valve is therefore independent of pressure variations
at the supply.
Setting the drive pressure regulator at 25.4 psi (175 kPa) allows for a maximum inspiratory
flow of 70 L/min at the ventilator.
1.8.3 Gas Box Assembly
The driving module consists of the proportional valve and a solenoid valve for the vent mode
switch. The proportional valve pressure regulator, and generates a driving gas flow of 0 - 70
L/min in relation to the control voltage of the proportional valve of 0 - 5VDC.
The control voltage of the proportional valve, required for the pre-selected parameter
settings, is generated by the BDU board. The driving gas flow Q
drive gas
is in the following
relationship with the tidal volume:
Q
drive gas
= V
T
/T
with: Q
drive gas
= driving gas flow
V
T
= generated tidal volume
T = time
1.8.4 Tube color coding
All the pneumatic tubes used in the AS3000 are color coded for use in the United States
only.
GAS US STANDARD
O
2
Green
N
2
OBlue
AIR Yellow
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