...
Slide the low-Z box back upstream to seat the O-ring. Then clamp the flange / O-ring / film assembly using the clamp.
Test that the two gas sections are separated again. To do this, check that the He flowmeter is at a high value (it reads H +F above 500) and decreasing. The initial high value is because there is heavier gas (air) being purged out of the Front end / I0 section. It should eventually settle around 200-240. If the flowmeter value is already lower than this, this means there is a hole in the film. This often happens because the O-ring can cut the film. No worries! Just unclamp the assembly, replace the film, clamp and test again!
Once the separation of the two sections is confirmed, retighten Retighten the two allen hex bolts in the back of the low-Z box using the 5/32" Allen wrench. This ensures that the box moves properly with the stage when you move the HORZ motor. If it is kept loose, the bellows will tend to oppose this HORZ motion and make scans with the HORZ motor not reproducible.
That's it! Make sure the flowmeter settles back down to 200-240 and wait 5 to 10 more minutes to ensure no air is in the front end. Then you can turn on the X-rays and continue!