3/4/98

Hi all I am a novice of this list, so please write me is there is some FAQ to avoid starting again old threads.

By the way, is there a consolidated way of protecting a SEM chamber from boost pressure coming from N2 bottle during venting?

(this may occur if someone accidentally moves the low pressure stage on the bottle)



Thank you in advance

Dr. Eng. Edoardo Bemporad, Ph. D.

Assistant Professor of Materials Science

University of Rome "Roma Tre" (Italy)

Dipartimento di Ingegneria Meccanica e Industriale

(Department of Mechanical and Industrial Engineering)

Via della Vasca Navale 79 - 00146 Rome, Italy

Tel: +39 6 5517.3293

Fax: +39 6 5517.3256

LIME Lab (InterDipartimental Laboratory of Electron Microscopy) Tel: +39 6 5517.3200

E-Mail:bemporad@uniroma3.it

I used a diver's demand valve to stop the N2 flow. The demand valve closes

when the instrument stops sucking - just like a diver only gets air while

sucking. As for removing the pressure regulator. I would expect that taping

the control and a sign "do not touch" would suffice. Lesser offenders have

suffered capital punishment.

Cheers

Jim Darley



ProSciTech Microscopy PLUS

PO Box 111, Thuringowa QLD 4817 Australia

Phone +61 7 4774 0370 Fax: +61 7 4789 2313

Great microscopy catalogue, 500 Links, MSDS, User Notes

www.proscitech.com.au

We have a demand valve on our TEM so that venting does not over-pressure

the column. Basically the valve allows N2 gas to enter the column as

long as it "sees" a negative pressure. As the pressure in the column

rises to atmosphere, the flow of N2 slows until it is at equilibrium

with the room. The same valve is used for venting the camera and the

column as the demand valve is part of the regulator on the N2 bottle.



Greg Strout

Electron Microscopist, University of Oklahoma

e-mail: gstrout@ou.edu

The easiest solution is to have a 'T' piece in the line connecting the N2

cylinder to the SEM, with the leg of the 'T' open to the atmosphere. Adjust

the N2 pressure so that there is a reasonable flow of N2 to atmosphere when

not venting. It's not precisely controlable but it stops over pressure

problems.



--

Larry Stoter

17, Rocks Park Road, Uckfield, E. Sussex, TN22 2AT, UK

email: LPS@teknesis.demon.co.uk

Phone/Fax: +44 (0)1825 767967

Overpressure in SEM chambers is only a problem on some SEMs with

airlocks for sample loading.

For direct loading SEMs, the stage door opens when the chamber is above

atomospheric if you don't fasten the door down.

On JEOL SEMs there is an overpressure relief valve on the N2 Backfill

line and some other SEMs also have an overpressure valve.



If you often vent the specimen chamber, just make sure the stage door

opens freely or that a port flange can pop open. Just loosen the port

flange screws. Atmospheric pressure holds these tight against the vacuum

so there is no need need for tightness except at the beginning of pump

down.



Ronald Vane

XEI Scientific

RVaneXEI@concentric.net

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