When I couldn't get better than 10-5 on my XP I naturally thought there was 
a leak.  What I eventually found was a speck of dust in the Penning guage. 
A gentle whiff of air fixed it.
Maybe this helps.
Regards
John

PS you can measure the flow of air from the exhaust of the analyser rotary 
pump to tell if there really is a leak.


----- Original Message ----- 
From: "Bernie Genna" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, August 04, 2005 6:54 PM
Subject: vacuum problem on Delta Plus


> 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
>


********************
John Lanham, Principal Scientific Officer
Stable Light Isotope Unit
Archaeology Dept.
Private Bag Rondebosch 7701
University of Cape Town
tel: +27 21 650 3847
fax: +27 21 650 2352
********************