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Kim:

 

I've had a look at my own EA. In reply to your questions:

 

1.	My aluminum blocks do not leak compressed air at all times. The only
time I hear the air leaking anywhere (or should I say that I've noticed) is
at the solenoids when it switches positions of the bimatic valve or the
autosampler. And technically, those aren't leaks, but venting.
2.	Can't say for sure. But on my EA, the regulator and gauge is after
the safety block and before the switching valve solenoids. Given that, the
safety block is at the higher input pressure, although a leak would reduce
that to some degree (but still equal to or higher than what the gauge
shows). In "theory", that should not cause a problem, unless it cannot
maintain the required pressure. I don't know if air pressure has to be 0 or
whether the safety cut-off will come into play if pressure merely drops to a
certain level. A leak downstream from the regulator would be seen with a
leak test, since it's a closed system (you know. close valve, watch gauge).
I would think a significant leak could affect the function of the
autosampler and the bimatic valve. At the very least, switching might become
slow and sluggish if pressure cannot be maintained or replenished fast
enough. Might this affect oxygen injection efficiency? Have you watched the
air pressure gauge to see how quickly it recovers when switching?
3.	O2 flow should not change. In inject mode it simply bypasses the O2
loop but still vents in the same place, although it might momentarily
fluctuate at actuation (see reply to next question).
4.	The pressure gauge probably will jump when the valve is actuated.
For a split second as the valve changes position, the flow may be
interrupted. Plus, on my EA at least, the He carrier and O2 pressures are
different, so there may be a slight pressure balance required during/after
switching.

 

I remember you posting about this before, but I don't recall your
troubleshooting measures to date. Have you tried installing a new GC column?

 

Hope you can sort out your problem soon. We don't want to see work-induced
diabetes developing.

 

--Alison

 


Alison Pye . [log in to unmask]

Stable Isotope Lab Coordinator
CREAIT . TERRA Facility . Stable Isotope Lab
<http://www.mun.ca/creait/TERRA/SIL.php> 
Alexander Murray Building
Memorial University of Newfoundland
St. John's, NL . Canada . A1B 3X5
ph: (709) 864-3217 . fax: (709) 864-2589
Please note new numbers.

  _____  

From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Kim Baublys
Sent: May 11, 2011 3:39 AM
To: Alison Pye
Subject: EA troubles: NA1500

 

Questions for NA1500 users.

 

I am still battling my EA which is smearing my sulfur peak over 200 seconds
instead of the usual 50.  I have tried all the usual things to no avail.

 

BUT I have now determined that I have a compressed air leak where the line
feeds into the EA. The culprit is the little double block of aluminium which
the compressed air and oxygen and He lines immediately feed into once
entering the EA.  The manual labels the blocks as a 'safety line' which
consists of a single effect microcylinder and two, 2 way single effect
microvalves.   The manual does not mention them at all in the spares list.
The air is coming out of the little hole at the top of the block and also
where both the blocks join together, which leads me to ask.  

 

1.	Is it normal for the aluminium blocks of the safety line to leak
compressed air at all times?

 

2.	Is this likely to cause enough of a problem to prevent the bimatic
valve operating properly? Given that the compressed air gauge at the front
of the EA reads as it should and is Teed in before the safety line.

 

3.	I have measured the oxygen flow at the oxygen vent at the front of
the EA and it is ALWAYS 25ml/min, even when doing an oxygen injection.
Should the flow from the oxygen vent slow down or stop when the bimatic
valve is actuated? 

 

4.	Could my poor peak be a result of the oxygen regulator not working
properly?  I notice that the pressure gauge gives a dramatic jump when the
bimatic valve is closed although this may have always happened. :-)

 

 

There is also a small leak in the micro-solenoid valve that powers the
sample carousel but this does not appear to cause any problems.

 

 

If anyone has any insights they would be greatly appreciated..  Because of
this I have become a highly valued customer at the lolly shop and I don't
think that that is good for my sugar levels  :-)

 

 

Regards

Kim

            

----------------------------------------------------------- 
Kim Baublys 
Stable Isotope Geochemistry Laboratory, Earth Sciences 
The University of Queensland, 4072 
Australia 

Ph   +61 7 3365 1131 
Fax +61 7 3365 1277 
http//www.uq.edu.au/geochem/