[RASMB] Rucurrent Dirty Lamp & Maybe Slow to Pump Down

[John Philo]

Peter, what, did Beckman sell you a lemon? It seems you have trouble
constantly.
 
Borries has a good point about pump oil and high temperatures, but my best
guess is that you still have a vacuum leak somewhere. Here is a 'rule of
thumb' leak diagnostic:
 
After the instrument has been through a couple of runs, and thus the water
vapor in the mechanical pump oil has worked its way out,  monitor the vacuum
reading during the initial pump down as the pressure drops through the
region from ~400 to ~200 microns. The successive readings (updates on the
CRT) should go down by ~1% of the previous reading. That is, it should go
like 400, 396, 392...306, 303, 300...204, 202, 200. The pattern won't
actually be that even of course, but you get the idea. 
 
When the instrument has been run a lot and things are really clean it should
go down even faster than that (perhaps ~1.5% per update). If the pressure is
dropping significantly less rapidly than this '1% rule of thumb' then that
is an indication you probably have a leak. 
 
As to leak location, to me the fact that the lamp is getting dirty so
quickly suggests the leak is right there at the lamp (despite the new lamp
o-ring).
 
John

  _____  

From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of Peter Edward Prevelige Jr
Sent: Thursday, February 16, 2012 1:56 PM
To: rasmb at rasmb.bbri.org
Subject: [RASMB] Rucrrent Dirty Lamp & Maybe Slow to Pump Down



Hi All -

 

I am having trouble with my lamp getting dirty after only a couple of days.
The instrument was just serviced. A new lamp and gasket  were installed
because of a vacuum leak and afterward the lamp intensity and noise level
looked great.

 

A couple of runs later the noise @280 was too high and when I checked the UV
intensity it was down to maybe 4K at the 230 peak. Cleaned  & aligned the
lamp and it was back up to 15K+ counts. Three days and 4 SedV runs and was
back down to 4K. Cleaned and aligned it and it is back up to 17K counts.  My
impression also is that it is slow to pump down but this is of course
subjective.

 

It seems like it is getting dirty much too fast. Certainly we never had to
clean it after every few runs. In any case, it seems to be getting dirty too
fast for a good Sed EQ run in the far UV at any rate. Any suggestions on
what to look for/do?

 

Thanks

 

Peter

 

 

 

 

Peter E. Prevelige Jr.

Professor

Dept. of Microbiology, BBRB 416/6

Univ. of Alabama @ Birmingham

845 19th St. South

Birmingham AL. 35294-2170

Phone 205 975-5327

FAX 205 975-5479

prevelig at uab.edu

http://www.microbio.uab.edu/faculty/prevelige/prevelige-p.htm

 

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