BIRD MARK 7 - Page 9

The NEEDLE VALVE ASSEMBLY is primarily
involved in providing the correct position for the
metering needle and its orifice (Fig. 12).
METERING FLOW OUT
METERING
FIGURE 12
The metering orifice in all Bird equipment consists
of straight, machined holes. Metering of gas is
accomplished by the amount of travel required
when the needle moves in or out of its orifice (Fig.
13).
METERING SLOPE
* METERING
NEEDLE
METERING ORIFICE
METERING ORIFICE
FLOW TERMINATION
(OFF)
FIGURE 13
Problems appear as the metering orifice begins to
“age”. As long as the orifice seat is sharply
defined, gas can be effectively stopped. After
many hard “shut offs’, an orifice seat may begin to
wear and not obstruct gas flow as required (Fig.
14). This leads to a constant leak in the circuit and
may cause the ventilator to malfunction.
NEW SHARP ORIFICE SEAT
OLD ORIFICE SEAT WORN BY
MANY HARD “SHUT OFFS”
FIGURE 14
8 INDEXED CAM STOP
Since the source gas is metered by the amount of
travel allowed the needle valve, it is important to
have precise control over that movement. The
INDEXED CAM STOP is utilized for limiting the
rotation of the control knob (Fig. 15).
SINGLE DUAL SIDE
INDEX INDEX VIEW
CAM CAMS
FIGURE 15
Pneumatic metering valves are the basic control of
all variable functions of time and flow in each Bird
respirator/ventilator. These valves control all.gas
flow being delivered to the patient or to the internal
circuits
of each piece of Bird equipment.
E HIGH PRESSURE CHECK VALVE
The CHECK VALVE was designed to assist in
directing gas flows within the timing circuits of Bird
equipment.
Gas flows into the inlet of the valve and physically
lifts the silicone sleeve off of its orifice, allowing gas
to proceed through the outlet to the internal cir
cuitry (Fig. 16). As backpressure builds up within
the circuit, pressure is transmitted backward to the
check vaive through the outlet port. This pressure
exeris the force required to push the silicone
sleeve down onto the orifice, obstructing gas flow
out of the circuit (Fig. 17).
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