rb6banjo wrote:
There is a valve on the front of the MS that you can open to release the vacuum after "venting" in the chemstation software. I'm with dblux. If you've never worked with an ms before, be sure to read everything - no matter how trivial you think it might be.
There is no valve on the 5971/5972 instruments for venting. On those instruments you went through the vent cycle in software to cool the oil diffusion pump, then once the pump and source were cool, you removed the column or slid the unit far enough away from the GC to remove the clamp on the interface and vent it there. You also had to remove the interface before you can remove the top plate and source/quad assembly. The vent valve was introduced with the 5973 models.
The rough pump should have an anti-suckback valve so that oil does not flow back up into the MS, but if they are old these can fail. Normally the helium flow of 1-2ml/minute is enough to allow the MS to come to atmospheric temperature in about 30 minutes without the backflow, but best to just remove the column when you turn off the power switch which stops the rough pump.
Do not vent the system between the rough pump and the diffusion pump, that will cause diffusion pump oil to suck back into the analyzer, and that is horrible to clean out of the system.