Exhalation Valve; Mechanical Overpressure Valve; Bleed Resistor - Datex-Ohmeda Aestiva 7900 SmartVent Technical Reference Manual

2 Theory of Operation

2.5.6 Exhalation valve

2.5.7 Mechanical
Overpressure Valve

2.5.8 Bleed resistor

2-26
The autoclavable exhalation valve manifold contains an elastomeric
diaphragm that is used along with the flow valve to control the pressures in
the breathing circuit. The manifold contains two male ports on the bottom for:
• Bellows drive gas
• Exhalation valve pilot
The manifold contains two female ports on top for:
• Drive gas (pass through)
• Drive gas return
• Bellows exhaust tube.
The female AGSS port comes out horizontally.
Pilot control of the exhalation valve is done with pneumatic connections
internal to the Aestiva 7900 Ventilator main pneumatic manifold. The valve is
normally open. Approximately 2 cm H
close the valve. When the exhalation port is open, gas flows from the bellows
housing to the scavenging port.
The Mechanical Overpressure Valve (MOPV) is a mechanical valve that
operates regardless of electrical power on or off. This valve has two functions.
First, it functions as a third level of redundancy to the ventilator's pressure
limit control functions, supplying pressure relief at approximately
110 cm H O.
2
Second, the MOPV valve functions as a backup in the event of a complete
blockage of the exhalation valve system, relieving circuit pressure at
approximately 30 cm H O under such failure conditions.
2
The bleed resistor is a "controlled leak" from 0 to 10 L/min in response to
circuit pressures from 0 to 100 cm H
exhausting through the bleed resistor permits control of the exhalation valve's
pilot pressure by modulation of the valve output. The bleed resistor exhausts
only clean drive gas and must not be connected to a waste gas scavenging
circuit. The output is routed away from the electrical components to make
sure that systems using oxygen drive gas meet the 10VA limitation
requirement for oxygen enrichment.
O of pilot pressure is necessary to
2
O. The small quantity of pneumatic flow
2
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