If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
In my volunteer work for a science workshop program, I'm upgrading their vacuum apparatus. Hope to get down to single-digit micron pressures in a plastic bell jar, to support a couple of kids's science fair projects. Last time I worked with vacuum was in the 1970's.
The intended setup is organized like , with these enhancements:
1. Pump is a donated Alcatel 2015 with KF-25 fittings. Rated flow 5 liters/second, with deadhead vacuum pressure 1e-4 torr. I hope it's in good condition inside.
2. Manifold is made from nominal 1/2" brass pipe nipples & a 1/2" ball valve. (We found a relatively good deal on KF-25 to 1/2" F-NPT adapters). I figure the conductance will be around 2 liters/second, but a wider path would need more money and/or volunteer hours. No TIG-welded stainless steel fabrication this year, unfortunately.
3. Would like to use the stock Nalgene belljar and ring gasket, with replacement baseplates. Each kid will get a baseplate & add his own feedthroughs. My plan of record is to use 1/2" hard plastic or 1/4" aluminum, about 8 inches square (belljar OD is about 6 inches), with a hole tapped for 1/2" pipe thread. A short nipple and KF-25 flange, loaned by the science workshop program, complete the baseplate.
General comments & advice would be welcome. Specific questions: *Plastic material recommendations? Would be nice if feedthroughs can be bare metal through hole sealed with glue. *Is there a handier way to adapt KF-25 hardware to a homemade baseplate? *Will flat belljar gasket tend to be sucked in? Does baseplate need ridges, roughening, or adhesive? Is neoprene sheet (e.g. from McMaster-Carr) suitable?
One way to make a slightly wider and much cleaner-looking manifold, perhaps with a 3/4 inch ball valve, is based on 3/4" rigid copper pipe. It can be soldered to a KF-25 brass half-nipple, after turning down or boring out one part by about 0.010. Anybody seen this done?
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
bell jar gaskets are best being a large, flat gasket that allows easy placement of the bell jr without allignment issues - it should cover most of the surface of the base plate, stopping at the pump intake fitting - then use some Vacuum Grease.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Feedthroughs as you describe will work for this application, small leaks (1E-6 torr) would be negligible for science fair projects, (although unacceptable for semiconductor mfg) and the plastic bell jar itself will outgas a little.
Stick with npt to KF-25 adapters, this is simple and works well.
The cross-section area of the neoprene sheet gasket will determine the force acting on it from atmospheric pressure. The bell jar will press down when under vacuum and tend to hold the gasket in place, a wider gasket will be much more reliable. Use of a silicone vacuum grease on the gasket underside surface will help. Don't score or roughen the baseplate. Solid neoprene sheet should work. RTV sheet will work.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Vacuum bell-jar baseplate issues
