Hi Bernie... A quick and easy test of the knife edge seal would be to spray some acetone along it. If there is a leak the acetone will be drawn into the mass spec and you will see a spike in your pressure. If no spike is observed (watch it closely as you spray the acetone...it can be quick) then your knife edge seal should be fine. Unless of course your vacuum gauge is faulty. Have your two turbo pumps on the ion source/analyzer system started fine? Are you in continuous flow mode...i.e. is your SGE valve open? If this is the case then a high pressure reading like you are experiencing is normal. Tim On Thursday, August 4, 2005, at 10:54 AM, Bernie Genna wrote: > Hi All, > > We have a Delta Plus XL Mass Spectrometer that we vented last > week to replace one of the quartz spacers in the source. While all the > parts we laid on the table overnight (we had to order the spacer), the > cooling unit in our building failed and the lab temp got up to 85 > degrees. We had inadvertently left our cooling water turned after > venting the instrument. When we reassembled the source and tried to > pump down, the source vacuum will only pump down to 5X10-5. Thermo > said that the source flange clamps were overtightened and the knife > edge seal that seals the source housing needed to be replaced. Well we > finally got the source flange clamps (from a secondary source), and > replaced the knife edge seal and see that the source vacuum is still > 10-5. The forevac vacuum is normal (2X10-3). My question(s): Could the > temperature difference between the cooling water (15 degrees) and the > air temperature (85 degrees) cause problems in the vented source > housing and/or exposed flight tube? Could the high vacuum gauge be > faulty? Do I suddenly not know how to tighten a source gasket to get > the proper vacuum? > > Any ideas will be very much appreciated. > > Bernie Genna > NCSU > ----------------------------------------------- Tim Prokopiuk B. Sc. Geology/Technician Saskatchewan Isotope Laboratory Room 241 Department of Geological Sciences University of Saskatchewan 114 Science Place Saskatoon, Saskatchewan, Canada S7N 5E2 Phone: (306) 966-5712 Fax: (306) 966-8593 Email: [log in to unmask]