Hi Joe
We have retrofitted all our instruments with foreline traps.  Some are off the shelf (BOC Edwards: Inlet accessories Foreline trap - Model: FL20K; Part #A13305000); others are in house built (cheaper).  The nice thing with the Edwards trap is it can be installed horizontally or vertically. For the NW10 flange (smaller pump) you need to get a reducing union (NW10 to NW25).  The charge sieve is fairly cheap to buy and comes in a one pound can.  The material can be reactivated by burning off the oil in a vented oven if needed.

The problem with the sieve is that it absorbs air and takes a long time to clear when first starting the system.  All you have to do is put the basket (for the Edwards FL20K) or the sieve beads into a beaker at 100oC for 1-2 hours.  Put the sieve back into the holder and pump immediately while hot.  The vacuum will go down to normal quite fast and normal operation will follow as if it wasn't there.

Rotary pumps have an anti-suckback valve to prevent oil from being sucked back into the turbos when a power failure occurs.  They do not work very well since the spring is always pulled 24/7 year round.  Failure on those pump valves is high.  The "modern" IRMS has a down to air valve on the side of the turbos that breaks the vac when powering down the system to prevent oil from being sucked up into the high vac area.  However the vac during operation at the top of a turbo is 10^-6 to 10^-9 mbar and the rotary is about 10^-3 mbar.  Oil vapour is going where the pull is hardest- the turbo, thus the foreline traps.  If the pipework above the rotary pump has oil in it, then it is sucking oil vapour.  When we do our yearly maintenance, all sieves are brownish to black, from the milky white original colour.  Thus, it works.  We have foreline traps on our instruments since 1999. All our previous older instruments had these traps by default from the manufacturer.

Gilles

Gilles St-Jean
Chercheur / Research Scientist
Université d'Ottawa / University of Ottawa
Sciences de la Terre / Earth Sciences
140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5
Tel: 1-613-562-5800 xt 6830 (Bureau / Office)
                    xt 6839 (Bureau / Office Lab)
                    xt 6836 (IRMS lab)
Téléc. / Fax: 1-613-562-5192
Courriel / E-mail: [log in to unmask]
Toile / Web: www.isotope.uottawa.ca
 
-----Message d'origine-----
De : Stable Isotope Geochemistry [mailto:[log in to unmask]] De la part de Joe Lambert
Envoyé : 13 novembre 2006 15:55
À : [log in to unmask]
Objet : [ISOGEOCHEM] High Vacuum Safety Valve

Hello Everyone,

     I'm writing to ask if anyone has taken the extra precaution to install
any type of oil trap between the roughing pumps and turbo pumps on any of
the Delta series IRMS's from what is now Thermo-Electron.  We have a Delta
Plus and recently encountered the problem of oil backstreaming into the
source turbo (Pfeiffer pumps).  We use a zeolite based oil/water trap for a
number of extraction lines where space is not an issue.  It would seem
somewhat hard to plumb this large of a trap into the compact IRMS.  Can
anyone recommend a smaller trap (NW-25 fittings) or a part number for an
additional anti-suck-back type valve?  We are currently unsure of the reason
for the oil backstreaming problem, but we certainly would like to protect
ourselves from future events.

Sincerely,

Joe Lambert
Alabama Stable Isotope Laboratory