NM2C REPLACEMENT PROCEDURES (continued)
4.7 Oxygen Supply Pressure Failure Protection Device
The oxygen supply failure protection devices (failsafe assemblies) are located
within the flowmeter housing. Access to these assemblies requires removal of
the rear cover. Figure 4-7 shows a typical arrangement of a failsafe assembly
and its connections.
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 the three
compression fittings.
4.7.11 Connect the flexible tubing to the control port, and install a new tie-
wrap clamp.
Rev. B
4-23
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