From: Geoff=Howlett%BioChem%UNIMELB@muwaye.unimelb.EDU.AU
  To  : rasmb@bbri.eri.harvard.edu
  Date: Wed, 20 Apr 94 8:43:11 +1000

...no subject...

Hi

I would like to thank all who responded to the question concerning speed 
limits for the filled-epon centerpiece.  Responses from John Philo (Amgen), 
Mike Jacobsen (Brisbane), Greg Ralston (Sydney), Preston Hensley 
(Smithkline), Peter Jeffrey (Canberra), Tom Laue (New Hampshire), Emory 
Brasswell (Yale) attest to the feeling on the subject and a spectrum of 
opinion.  Rather than attribute comments and risk violating individual  
"centerpiece warranties" I summarise:

1. We don't tighten more than recommended (120psi) and have done a number of 
60K runs.  Eventually the centerpiece will break. Have seen strange effects 
using Aluminium (Aluminum) centerpieces 

2. Have done about 4 runs at 55-60K without obvious irreversible effects

3. Have seen a septum pop out at 52k and a window crack.  We don't go past 
42k with filled epon. Have bought aluminium DS centerpiece instead.

4. We use all centerpieces at all speeds with no problems or extra precautions

5. We tighten to 140 psi and have occasionally resorted to vacuum grease to 
stop leaks at 60k

6. We routinely use carbon filled epon at 60k.  If there is a leak one side 
the rib will crack. We tighten to 120 psi and many of our centerpieces have 
gone for years without problems.  Can check warping of the centerpiece using 
alignment tool.

7. Can use filled epon at 60 k for a while.  Should probably torque to 155-
160.  Could run equilibrium runs for longer at a lower speed and longer 
column.  May take 48 hours.

Needless to say on the basis of this expert opinion I did my first run at 60k 
yesterday ( I tightened to 130psi) and it worked fine.  

Its a great way to show non-sedimenting OD.

Cheers and thanks to all the respondents.

Geoff Howlett