
REPLACEMENT PROCEDURES (continued)
NM2B
4.7
Oxygen Supply Pressure Failure Protection Device
The oxygen supply failure protection devices (failsafe assemblies) are located
behind the gas instrumentation panel. Access to these assemblies requires
removal of the rear cover. For earlier machines, replacement assemblies are
supplied with all hardware out to the first compression fitting in each line.
On later machines with flowmeter assemblies having an Oxygen Ratio
Controller (ORC), failsafe assemblies have an additional inlet port that allows
both pipeline and cylinder supplies to be connected directly to the failsafe
assemblies. Figure 4-7 shows the arrangement for both types of assemblies.
4.7.1
Disconnect all pipeline hoses and set the System Power switch to ON.
4.7.2
Close all cylinder valves except the O
2
valve.
4.7.3
Set the oxygen flow to 5 liters per min.
4.7.4
Open the other gas flow control valves to drain pressure from the
system.
4.7.5
Close the O
2
cylinder valve and the O
2
flow control valve. Press the
O
2
Flush valve to drain oxygen pressure from the system.
4.7.6
Set the System Power switch to
STANDBY
.
4.7.7
Remove the screws holding the rear cover, and remove the cover.
4.7.8
Cut the tie-wrap clamp on the flexible O
2
control line, and disconnect
the flexible tube.
NOTE:
On later machines with assemblies that have brass fittings instead
of nylon, the flex tubing is attached with a press-on hose clamp
instead of a tie strap.
4.7.9
Disconnect the compression fittings at the side ports and at the check
valve, and remove the assembly.
NOTE:
If fittings must be installed in the replacement block assembly, use
Loctite #271 (red). See parts list in Section 8.
4.7.10
Install the replacement failsafe assembly, and tighten all compression
fittings.
4.7.11
Connect the flexible tubing to the control port, and install a new tie-
wrap clamp.
Rev. C
4-22
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