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9. Turn the shaft of the valve so that oxygen starts to fl ow. Adjust the fl ow
to the prescribed Basal fl ow level (still holding the gear and stop arm in
position). When this is achieved, tighten the two grub screws on the stop
arm.
10. The stop screw height must now be adjusted. Turn the valve a full turn
counterclockwise and check that it just clears the top of the stop screw. If
not, adjust the stop by screwing it in till the arm JUST clears and tighten
the lock nut. Check that the arm hits the stop when turned clockwise and
clears the top when turned counterclockwise.
11. The ‘Idler gear’ must now be meshed to link the two valves. Turn the
stop arm clockwise to the stop and hold, and turn the oxygen gear fully
counterclockwise, (as in Step 8). This should give you the ‘basal fl ow’
showing on the oxygen fl ow meter. Turn the nitrous oxide fl ow up to
approximately 400 ml and, while holding the stop and gear in position,
carefully insert the idler gear and its bush onto it’s shaft. Meshing it’s teeth
with the oxygen and nitrous oxide gears, then fi t the idler gear nut.
12. Carry out a full check of the hypoxic guard calibration as described in
Chapter 4.
5.3 Setting Oxygen Basal Flow
If the Basal fl ow has altered during normal use (this can occur if the valve
has been turned down with excess force, reducing the fl ow), or has increased
(sometimes due to settling in of the regulators), the following method can be
used to restore the correct fl ow, often without the need to recalibrate the entire
hypoxic guard block.
1. Remove the front cover (Section 5.1). Turn all fl ow controls to minimum.
Turn the machine on and allow basal fl ow on the oxygen to stabilize for a
few minutes.
2. There are two grub screws holding the oxygen stop arm to the valve
shaft. Hold the stop arm tight against the stop screw and slightly slacken
the two screws. Turn the valve shaft until the basal fl ow is within limits and
retighten the grub screws.
Detailed Repair Procedures
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