HI Chris--

You'd rather not over-tighten them, but that would show up as 
puckering.  I'm guessing the needle tip is bent  a little out of shape.  
The end should bend in a little, similar to Hamilton uL syringes.  
Sometimes they get bent back or blunted.  Alltech (excuse me, Grace 
Discovery) had a sharpening stone for needles, and others might too, 
just be careful using it.  Me, I just use a small pliers to bend it in.

To make your own, you can look at:
http://isogeochem.wikispaces.com/Sampling+needle

take care,

gerry

On 6/24/2011 2:06 PM, Christopher Maupin wrote:
> Dear Listers,
>
> We're encountering a problem with our gasbench measuring needle. It's 
> clogging every 2 days or so with usually single but sometimes multiple 
> pieces of septa. We run carbonates (acidified by hand), primarily, as 
> well as waters. When the needle isn't clogged we get exceptional 
> precision using carefully weighed sample sizes. Are we tightening the 
> exetainer caps too tight? Not tightly enough? I have tried different 
> needle tip shapes. The exetainer/cap/septa product code is 9RK8W 12mL 
> BORO x 100 from Labco, and the needle is the OEM thermo measuring needle.
>
> Thanks!
> Chris
>
> _____________________________
> Chris Maupin
> Paleoclimate Lab, JGB 5.118
> Jackson School of Geosciences
> University of Texas at Austin
> 1 University Station C1100
> Austin, TX 78712
> [log in to unmask]
> Stable Isotope Lab: 512-232-4184
> http://www.ig.utexas.edu/people/students/maupin/
>