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
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?

 

  1. 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.

 

  1. 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?

 

  1. 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. J

 

 

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  J

 

 

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/