2 Theory of Operation
M1207026 2-7
2.2.3 Flow control Needle valves (one for each gas) adjust gas flow. Clockwise rotation
decreases flow. Counterclockwise increases flow. A hypoxic guard
system sets the maximum ratio of N
2
O to O
2
.
WARNING The hypoxic guard sets a minimum O
2
concentration in
the common gas stream.
Hypoxic guard system The hypoxic guard is an internal system that is not serviceable. It
helps control an approximate minimum 1 to 3 ratio of flow between O
2
and N
2
O. When engaged, the O
2
and N
2
O knobs turn together:
• An increase in N
2
O flow causes an increase in O
2
flow.
• A decrease in O
2
flow causes a decrease in N
2
O flow.
Higher concentrations of O
2
are possible when the hypoxic guard is
not engaged: either by reducing the N
2
O flow below the point of
engagement or by increasing O
2
flow above the point of engagement.
When the N
2
O flow is below the point of engagement, increasing the
N
2
O flow turns the O
2
sprocket without changing the O
2
flow. Once
the guard is engaged, turning the N
2
O flow control counterclockwise
(increase in N
2
O flow) also turns the O
2
knob counterclockwise
(increase in O
2
flow) to maintain a nominal 25% minimum O
2
concentration.
Decreasing the N
2
O flow from the engagement point rotates the O
2
sprocket away on the O
2
knob, increasing the O
2
concentration.
M1207027 004 MANUAL−DOC, Technical Reference Manual, Technical Reference Manual for 9100c, English−default
Reproduced from the electronic master in MATRIX
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