Prima 451 – User Manual 9
Description
3.4
Mechanical
A
HD (Anti-h
ypoxic de
v
i
c
e)
3.4.1
I
n
t
r
odu
c
t
i
on
The Mechanical AHD is housed within the flowmeter module
and controls the relative flow rates of oxygen and nitrous
oxide.
A predetermined minimum oxygen concentration of 30% ±3%
in the oxygen / nitrous oxide mixture is maintained over the
flow range to prevent delivery of a hypoxic mixture.
3.4.2 Gas Delivery Switch (1)
The gas delivery switch (1) operates on the oxygen supply
and must be in the ‘On’ position for normal operation of the
anaesthetic machine.
Switch labelling: I indicates On
0 indicates Off
The switch consequently controls the supply of all gases
provided with a gas cut-off triggered by a predetermined
pressure level within the oxygen supply (see section 3.3.1).
The whistle functions continuously for a minimum of seven
seconds if the oxygen supply fails.
3.4.3 Gear Linkage -
Nitrous
O
x
i
d
e C
on
t
r
o
l
Gears connect the nitrous oxide control knob to an internal
oxygen needle valve. This ensures that there is always a
minimum oxygen concentration of 30% ±3%. This ratio is valid
at all flow rates.
3.4.4 Oxygen Basal
F
l
o
w
To allow the system to function correctly, an oxygen basal
flow is continuously supplied.
Single flow tubes: 100 - 200
m
l
/
m
i
n
Dual cascade
s
ys
t
e
m
flow tubes: 50 - 75
m
l
/
m
i
n
This basal flow can only be turned on and off by using the Gas
Delivery Switch.
C
A
U
TIO
N
The oxygen control is restricted to prevent the needle valve
from fully closing. This ensures a minimum oxygen basal
flow.
DO NOT attempt to close the flow to zero. Do not
overtighten the knob.
3.5 Pressure
G
a
ug
e
s
Pressure gauges (50 mm diameter) are located on the front
panel below the flowmeter bank (1).
The gauge for Air is positioned between oxygen and nitrous
oxide. Unused gauge positions are blanked out.
All pressure gauges are colour coded and labelled for the
gases whose pressures they are indicating.
The gauges are calibrated in kPa x 100.
1
1
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