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 #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
its times like these when 4HV saves me from so much trouble.
As per Mattski's point I will make a steel water pipe vacuum vessel, 2 in OD laying on its side, half filled and 3 feet long. If half filled with vaccuum and half filled with oil it will have greater surface area then just a cylinder's circlular area standing on end. this would speed up and increase the drying effciency at the expense of pulling a vac on much greater volume.
as Ash has said, a rotary vane pump is what I will use.
I geuss flexible tubing is out of the question, so the pump and vessel must be held together with rigid pipe, and supported carefully? Flexible steel braided rubber flex pipes are tempting, but I presume I can kiss 100 microns good bye if I use such a tube?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
GluD wrote ...
The greater volume shouldnt be a concern I think. My two stage rotary vane pump can pull out 70 liters per minute. At least it says so on the paper.
Yes but with my previous experience the harder the vacuum, the longer it takes. Just based on the fact you and I depend on piston/rotary vane pumps, which are inherently limited (due to kinetics ), versus turbo-molecular pumps.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
.I geuss flexible tubing is out of the question, so the pump and vessel must be held together with rigid pipe, and supported carefully? Flexible steel braided rubber flex pipes are tempting, but I presume I can kiss 100 microns good bye if I use such a tube?
Flexible re-inforced tubing is often used for forelines (rotary vane pumps), so don't rule this option out just yet.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Flexible re-inforced tubing is often used for forelines (rotary vane pumps), so don't rule this option out just yet.
I f I could get away with this it would save me from such headaches and trouble!
Carl Pugh wrote ...
One thing that you might be careful of is that Oil that has all the dissolved air removed has a high breakdown voltage. Oil that does not have any of the air removed has a high breakdown voltage. Oil that has some of the air removed has a much lower breakdown voltage.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Patrick wrote ...
Ash Small wrote ... Flexible re-inforced tubing is often used for forelines (rotary vane pumps), so don't rule this option out just yet.
I f I could get away with this it would save me from such headaches and trouble!
I don't see why not. Here's a report I'm personally familiar with, showing vacuum of 50 microns readily achieved in a gallon-size vessel using rotary vane pump and ordinary flex tubing (not spiral reinforced vacuum hose).
Your horizontal pipe idea is good, not only to maximize the oil surface area but to minimize its depth. If half full of oil, the hydrostatic pressure at the bottom will be about 2000 microns, even if pipe is pumped to a perfect vacuum. You're right that heating the oil while under vacuum will speed up the drying and degassing. I have thought about drying my oil in small batches in a metal pan, that could sit inside the vacuum pot and be separately heated. (when in doubt I tend to be over-conservative, rather than try the fast way and improve if necessary).
Carl told me that in commercial practice, oil is often admitted to an evacuated transformer tank through a spray nozzle in the top, giving dissolved moisture and air a good final chance to escape. In a vacuum pot you could even circulate the oil mechanically with an external pump, drawing it out from the bottom and spraying it back in from the top.
Patrick wrote ...
Carl Pugh wrote ...
One thing that you might be careful of is that Oil that has all the dissolved air removed has a high breakdown voltage. Oil that does not have any of the air removed has a high breakdown voltage. Oil that has some of the air removed has a much lower breakdown voltage.
Can anyone back up Carl Pugh's thoughts here?
Sounds plausible. What matters to you is not whether your oil's breakdown voltage is maximized, it's whether it meets your absolute requirement. Why not make a dielectric-strength test cell with gap (between slightly convex electrodes) small enough to test with a NST?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Klugesmith wrote ...
Your horizontal pipe idea is good, not only to maximize the oil surface area but to minimize its depth. If half full of oil, the deepest fluid will have an absolute pressure of 2000 microns due to weight of overlying oil, even if pipe is pumped to a perfect vacuum.
Yes, these two facotors length for SA, and shallow depth, were why I thought steel pipe idea up. The wheight of overhead oil, I had not considered. Now the pipe is steel thick wall, 1.4 ID, half full will have 0.7 inches of oil at the deepest,the pipe would then be as long as needed for a useful volume for each run.
Klugesmith wrote ...
You're right that heating the oil while under vacuum will speed up the drying and degassing, but that would greatly reduce the strength of PVC pipe if that's what you're planning to use.
Its going to be threaded, sealed thick wall steel pipe now, not plastic, and later i can choose too heat it, externally, which eliminates the need for wires to pierce the vacuum vessel.
Klugesmith wrote ...
Carl told me that in commercial practice, oil is often admitted to an evacuated transformer tank through a spray nozzle in the top, giving dissolved moisture and air a good final chance to escape. In a vacuum pot you could even circulate the oil mechanically with an external pump, drawing it out from the bottom and spraying it back in from the top.
Spray nozzel, if this works maybe others can pursue that idea.
Klugesmith wrote ...
What matters to you is not whether your oil's breakdown voltage is maximized, it's whether it meets your absolute requirement. Why not make a dielectric-strength test cell with gap (between slightly convex electrodes) small enough to test with a NST?
An Acrylic + two 1" balll bearings sumbmerged in oil energized by a Variac+NST with HV voltmeter has already been built, for this project. Quality control matters.
Klugesmith, is that source you cite, just using common tubing from the hardware store?
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Patrick wrote ...
James wrote ...
The vacuum bible:
Ooooooo! Sams faqs are great i shouldhave been smart enough to check this on my own
Patrick - I've been degassing dielectric oil for X-ray tube heads for about 12 years, and I'd be happy to tell you about my vacuum system and process that I use. I use a very large glass bell-jar (with safty cage) and a Welch model 1397 2-stage vacuum pump. A diffusion pump is not necessay.
Later today I'll post a picture of my vacuum system, and I'll give you some details about te process that I use for degassing. Right now I can't spend any time on 4hv because of my huge backlog of work that's been piling up. But I will get back here later this evening (Minnesota time).
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.
100 micron Vacuum drying dielectric oil...
